JL · AP MICROECONOMICS

Unit 1 · Basic Economic Concepts

基本经济概念 — 稀缺性、经济体制、PPC、比较优势、成本收益与边际分析 · 对应 CED 1.1–1.6 · 选择题占比约 12–15%

本单元学习目标 LEARNING OBJECTIVES

解释稀缺性如何迫使人们做选择，并正确计算机会成本 · Explain scarcity and calculate opportunity cost
识别四种生产要素及其报酬 · Identify the factors of production and their payments
比较市场经济、计划经济与混合经济如何配置资源 · Compare how market, command, and mixed economies allocate resources
用 PPC 表示效率、机会成本与经济增长，并判断曲线移动 · Use the PPC to show efficiency, opportunity cost, and growth
区分绝对优势与比较优势，求出互利的贸易条件 · Distinguish absolute vs. comparative advantage; find mutually beneficial terms of trade
用总量与边际两种方法找最优选择（MB = MC），并应用效用最大化法则 · Find the optimal choice using total and marginal analysis; apply the utility-maximizing rule

Term 术语	Meaning 含义	中文
Scarcity	Unlimited wants vs. limited resources — we cannot have everything we want	稀缺性
Opportunity Cost	The value of the next best alternative given up	机会成本
Trade-off	Getting more of one thing means getting less of another	权衡取舍
Factors of Production	Land, labor, capital, entrepreneurship; most are scarce, but non-rival knowledge may not be	生产要素
Physical / Human Capital	Man-made tools & machines / workers' skills, education, health	物质资本 / 人力资本
Market / Command / Mixed Economy	Resources allocated by prices / by central planning / by both	市场 / 计划 / 混合经济
Production Possibilities Curve (PPC)	All maximum combinations of two goods an economy can produce with given resources and technology	生产可能性曲线
Efficiency	Productive: on the PPC; Allocative: the point society values most	效率（生产 / 配置）
Absolute Advantage	Can produce more with the same resources (or the same output with fewer resources)	绝对优势
Comparative Advantage	Can produce at a lower opportunity cost	比较优势
Terms of Trade	The rate at which one good is exchanged for another	贸易条件
Explicit / Implicit Cost	Out-of-pocket payment / value of forgone opportunity (no payment)	显性 / 隐性成本
Marginal Benefit (MB) / Marginal Cost (MC)	Additional benefit / cost of one more unit	边际收益 / 边际成本
Marginal Utility (MU)	Additional satisfaction from one more unit; usually diminishing	边际效用
Sunk Cost / Fixed Cost	Already paid, or the same no matter what you choose — does not affect the optimal quantity	沉没成本 / 固定成本
Positive / Normative	Describes what is (testable) / what ought to be (value judgment)	实证 / 规范
Traditional Economy	The three basic questions are answered by custom and tradition	传统经济
Incentive	A reward or penalty that motivates behavior	激励
Ceteris Paribus	“All other things held constant” — the key assumption of economic models	其他条件不变
Utility	Satisfaction a consumer gets from consumption (measured in utils)	效用
Budget Constraint / Budget Line	All combinations a consumer can afford with given income and prices	预算约束 / 预算线

考试结构 EXAM FORMAT AP Micro 考试：Section I 60 道选择题 / 70 分钟（占 2/3）；Section II 3 道 FRQ（1 长 2 短）/ 60 分钟（占 1/3）。Unit 1 在选择题里大约 7–9 道；FRQ 中的 PPC 与比较优势经常以短题形式出现。

1.1Scarcity 稀缺性

经济学研究的起点只有一句话：人的欲望是无限的，而资源是有限的。你想要新手机、想出国旅游、想周末睡到中午，还想周末补课提分——但钱、时间、精力都有限。这种“不够用”就是 scarcity（稀缺性）。

时间是最公平的稀缺资源——每个人每天都只有 24 小时。多做一件事，就一定要少做另一件事（trade-off）。

稀缺 → 选择 → 机会成本：Unit 1 的主线

定义 DEFINITION Scarcity: the condition in which limited resources are not enough to satisfy unlimited wants.
Economics is the study of how individuals, firms, and societies allocate scarce resources to satisfy wants.

稀缺 ≠ 稀少 ≠ 短缺

稀缺（scarce）：只要得到它需要放弃别的东西，它就是稀缺的。大米很多，但你买米要花钱，所以大米仍然稀缺。
不稀缺的东西（free good）：得到更多也不需要放弃任何东西，例如在海边呼吸空气。
短缺（shortage）是 Unit 2 的概念：某个价格下需求量 > 供给量。短缺是暂时的市场现象，稀缺是永远存在的基本问题。

考纲细节 · 不是所有生产要素都稀缺（CED MKT-1.A.2）土地、劳动、资本大多是稀缺的：一块地拿去盖工厂，就不能同时种菜。但有些要素，例如已经存在的知识（established knowledge）——勾股定理、一种成熟的流水线组织方法、一份公开的菜谱——可以被无数人同时使用，你用了并不会让别人少用一点。这种性质叫 non-rival（非竞争性），所以这类要素可能并不稀缺。

真题考法：“Which of the following describes a factor of production that is not fully scarce and that can be used simultaneously in the production of more than one good?” → 答案是 “Basic knowledge that enhances the organization of all manufacturing assembly lines”。

Micro vs. Macro · Positive vs. Normative 两组基本分类

这两组概念出自教材 Krugman Module 1.1，考纲没有单列，但选择题偶尔会考判断，而且后面每个单元都会用到“微观/宏观”的说法。

	研究什么	例子
Microeconomics 微观经济学	个人（household）、企业（firm）和单个市场如何做选择	奶茶店该定什么价？你该不该打工？最低工资会怎样影响快餐店雇人？
Macroeconomics 宏观经济学	整个经济的总体表现	今年通胀率是多少？为什么会经济衰退？央行加息会怎样影响失业率？

	特点	例子
Positive 实证	描述“是什么 / 会怎样”，可以用数据检验对错	“提高最低工资会减少青少年就业。”（可能对，也可能错，但能检验）
Normative 规范	表达“应该怎样”，含价值判断，无法用数据证明	“政府应该提高最低工资。” “贫富差距太大是不公平的。”

技巧 · 一眼判断看到 should / ought to / better / worse / fair / unfair 多半是 normative。注意：一句 positive statement 即使是错的，它仍然是 positive——判断标准是“能不能检验”，不是“对不对”。

Opportunity Cost 机会成本

定义 DEFINITION Opportunity cost = the value of the next best alternative forgone when a choice is made. 机会成本 = 放弃的选项中“最好的那一个”的价值

关键词是 next best（次优）：只算你放弃的选项里价值最高的那一个，不是把所有放弃的选项加起来——因为就算不选现在这个，你也只能做另外一件事。

WORKED EXAMPLE 1用“个数”表示机会成本原创

Lin has $30 to spend this weekend. A cup of bubble tea costs $5 and a movie ticket costs $15.

💰

$30 全买奶茶

🧋🧋🧋🧋🧋🧋

6 杯

💰

$30 全买电影票

🎬🎬

2 张

(a) What is Lin's opportunity cost of one movie ticket, in cups of bubble tea?
(b) What is her opportunity cost of one cup of bubble tea, in movie tickets?

(a) 买 1 张电影票（$15）就少了 $15，也就是少买 15 ÷ 5 = 3 cups of bubble tea。

(b) 买 1 杯奶茶（$5）就少了 5/15 = 1/3 movie ticket。

规律：两种东西的机会成本互为倒数（3 和 1/3）。经济学里机会成本常常用“放弃了多少个另一种东西”来表示，而不是用钱。这一点在 PPC（1.3）和比较优势（1.4）里会反复用到。

LAB 1机会成本选择器 · Which one do you give up?

周六晚上你只有 3 个选择（只能选一个）。点击你要选的那个，看看它的机会成本：

点击一个选项。

易错 TRAP · “免费”的东西也有机会成本演唱会门票是免费的，但你去了演唱会就不能打工，所以去演唱会的机会成本是 $90，而不是 $0。Free ≠ costless. 同理，“免费”的公共教育、“免费”的午餐，都要耗费稀缺资源。

WORKED EXAMPLE 2上大学的机会成本原创 · AP 经典考法

Ava is deciding whether to attend college for one year. Tuition is $20,000, books cost $1,000, and room and board cost $10,000. If she does not attend college, she will work full-time and earn $30,000, and she would still pay the same $10,000 for housing and food. What is Ava's opportunity cost of attending college for one year?

① 只算“因为上大学才多出来”的成本：学费 $20,000 + 书本 $1,000 = $21,000（显性成本）。

② 加上放弃的最佳选择：放弃的工资 $30,000（隐性成本）。

③ 食宿不算：不上大学她也要付同样的 $10,000，这笔钱不是因为上大学才花的。

答：$20,000 + $1,000 + $30,000 = $51,000。

想一想 · 为什么顶尖运动员常常不上大学？ 2003 年，18 岁的 LeBron James 高中毕业直接进了 NBA。对普通学生来说，上大学的机会成本是几万美元的工资；对他来说，上大学意味着放弃 NBA 合同和球鞋代言——机会成本高达数千万美元。同一个选择，对不同的人机会成本完全不同，所以“理性”的选择也不同。反过来，经济不景气、工作难找的年份，读研究生的人往往变多：放弃的工资变少了，读书的机会成本下降了。

Factors of Production 生产要素

经济学里的“资源”专指用来生产商品和服务的四类 factors of production。每一类要素被使用时都会得到一种报酬（这是 Unit 5 要素市场的伏笔）：

Factor 要素	What it is 含义	Examples 例子	Payment 报酬
Land 土地	All natural resources — “gifts of nature”	soil, forests, oil under the ground, fish in the ocean, minerals	Rent 租金
Labor 劳动	Human physical and mental effort	a cashier's working hours, a teacher's teaching	Wages 工资
Capital 资本	Man-made goods used to produce other goods (physical capital)	machines, tools, factories, delivery trucks, a pizza oven	Interest 利息
Entrepreneurship 企业家才能	Organizing the other factors, taking risks, innovating	the founder who risks savings to open a café	Profit 利润

例子图 · 一杯奶茶背后的四种生产要素

🌱

Land 土地：店面所在的那块地、种茶叶的茶园、产牛奶的牧场、制冰用的水

→ Rent 租金

🧑‍🍳

Labor 劳动：店员摇奶茶、收银、打扫卫生的时间和体力

→ Wages 工资

⚙️

Capital 资本：封口机、制冰机、收银系统、店面装修

→ Interest 利息

💡

Entrepreneurship 企业家才能：老板发现商机、决定开在哪里、研发新口味，并承担亏本的风险

→ Profit 利润

💵

老板账户里的 20 万启动资金：钱本身做不出奶茶，它是用来购买上面这些要素的

不是生产要素

PHYSICAL CAPITAL 物质资本

人造的生产工具

机器、厂房、电脑、货车。它本身不被消费，而是用来生产别的东西。

HUMAN CAPITAL 人力资本

劳动者身上的“技能存量”

教育、培训、经验、健康。人力资本提高的是劳动的质量（劳动生产率）。

易错 TRAP · 钱不是资本经济学里的 capital 指实物生产工具。Money、stocks、bonds 属于 financial capital（金融资本），不是生产要素——钱本身不能生产任何东西，它只是用来买生产要素的工具。题目问“Which is an example of capital?”时，选机器/工厂，不选钱。

LAB 2生产要素分类 · Sort the Resources

给每一项选一个类别，选完立刻显示对错和理由。（得分：0 / ）

练习 Practice 1.1

以下为历年 AP 真题（最后一题为原创补充），点选项即时判分并显示解析。

1.1-12012 AP Micro Q47

In which of the following situations is a good NOT scarce?

Consumers give up nothing to obtain more of the good.
Consumers can purchase as much of the good as they want at its current market price.
Large quantities of the good are available in the marketplace.
There is a surplus of the good at some positive price.
There is a shortage of the good at some positive price.

稀缺的判断标准：得到更多是否需要放弃别的东西。只有 (A) 不需要放弃任何东西。(B)(D) 有“价格”就意味着要放弃钱；(C) 数量多不等于不稀缺；(E) 短缺是市场现象。

1.1-22010 AP Micro Q1

Opportunity cost is defined as

excess demand for a good
unlimited resources and unlimited wants
a comparative advantage in the production of a good
the value of the next best alternative that is forgone when an activity is pursued
the value of all other possible alternatives that are forgone when an activity is pursued

机会成本 = 次优选择（next best）的价值，只算一个。(E) 把所有放弃的选项加起来，是最常见的错误。

1.1-32012 AP Micro Q46

After graduating from high school, Peggy Smith decided to enroll in a two-year program at the local community college rather than to accept a job that offered a salary of $12,000 per year. If the annual tuition and fees are $4,600, the annual opportunity cost of attending the community college is

$4,600
$7,400
$12,000
$16,600
$24,000

机会成本 = 学费 $4,600（显性）+ 放弃的工资 $12,000（隐性）= $16,600。

1.1-42013 AP Micro Q1

After graduating from high school, Maria chose to go to college, while Omar chose to work full-time. Which of the following best describes the opportunity costs for these decisions?

Maria’s opportunity cost includes the salary she could have earned if she had gone to work.
Maria’s opportunity cost is her living expenses while attending college.
Omar’s opportunity cost is the salary he will earn from working.
Omar’s opportunity cost is the tuition and expenses he would have paid for college.
Omar’s opportunity cost is definitely greater than Maria’s.

Maria 上大学的机会成本包括她本可以赚到的工资。(B) 生活费无论上不上学都要花；(C) Omar 赚的工资是他的收益，不是成本；(E) 机会成本因人而异，无法断定谁更大。

1.1-52005 AP Micro Q46

An opportunity cost is entailed in which of the following situations?
I. A student decides to attend college full-time.
II. A family uses its $20,000 savings to purchase an automobile.
III. A farmer decides to grow more wheat and less corn.

I only
II only
III only
I and III only
I, II, and III

三种情况都在稀缺资源之间做选择：上大学放弃工资；用积蓄买车放弃利息或其他用途；多种小麦就要少种玉米。只要做选择，就有机会成本。

1.1-62023 AP Micro 国际卷 Q38

Which of the following is an example of physical capital?

Earnings from a job
Fish in the ocean
Money in a person’s wallet
An unskilled worker
A tractor used in farming

物质资本 = 人造的生产工具，拖拉机。(A)(C) 是钱，(B) 是自然资源（land），(D) 是劳动。

1.1-72024 AP Micro Q7

Martina has $25 that can be used to either buy a new pair of shoes or a new sweater. She decides to buy the new pair of shoes. Martina's decision not to buy the new sweater represents which of the following concepts?

Opportunity cost
Income effect
Fixed cost
Diminishing marginal utility
Diminishing marginal returns

放弃的毛衣就是买鞋的机会成本。

1.1-82025 AP Micro 国际卷 Q1

Which of the following describes why scarcity exists in an economy?

There are more resources available than are being used.
Society’s resources are underutilized.
Society’s wants exceed its available resources.
Prices of available resources are lower than consumers’ willingness to pay.
Prices of available resources are higher than consumers’ willingness to pay.

稀缺的根源是欲望超过可用资源。(A)(B) 描述的是资源闲置，不是稀缺。

1.1-9原创

Which of the following is a normative economic statement?

An increase in the price of gasoline will reduce the quantity of gasoline demanded.
The unemployment rate rose to 5 percent last year.
The government should lower taxes on small businesses.
Higher tuition reduces the number of students who apply to college.
Trade between two countries can increase total output.

1.2Resource Allocation & Economic Systems 资源配置与经济体制

既然资源稀缺，每个社会都必须回答三个基本问题：

WHAT

生产什么？生产多少？

What goods and services to produce, and how much?

HOW

怎么生产？

Which resources and technology to use? 多用人还是多用机器？

FOR WHOM

为谁生产？

Who gets the goods and services? 产出怎么分配？

不同的 economic system（经济体制），就是回答这三个问题的不同方式。

WORKED EXAMPLE 3一辆自行车：三个基本问题由谁回答？原创

Compare how a market economy and a command economy would answer the three basic questions for bicycles.

	Market economy 市场经济	Command economy 计划经济
What 生产什么、多少	共享单车火了、价格和利润上升 → 企业自己决定多生产哪种车	计划部门定下“今年生产 500 万辆 28 寸自行车”
How 怎么生产	企业选成本最低的方法：工资高就多用机器人，工资低就多用工人	计划部门规定用哪个工厂、多少工人、什么设备
For whom 给谁	愿意并且付得起市场价格的人	按计划分配，例如凭票购买、按单位分配

关键区别是协调机制：市场靠价格把千千万万个人的决定协调起来；计划经济靠政府的指令。

	Market Economy 市场经济	Command Economy 计划经济
谁做决定	Individuals and firms 个人和企业，通过市场自愿交换	Government / central planners 政府集中计划
资源归谁所有	Private ownership, property rights protected 私有产权受保护	Public (state) ownership of the means of production 公有
靠什么协调	Price system — prices signal what to produce 价格机制	Production quotas and central plans 生产指标
激励	Profit and self-interest 利润与自利	Orders, plans, quotas
优点	效率高、竞争促创新、个人选择自由	更容易实现收入平等、容易提供公共物品
缺点	收入不平等、经济衰退时失业、公共物品供给不足	缺乏激励和竞争 → 效率低；个人选择受限；长期短缺或过剩

第三种：Traditional Economy 传统经济按习俗和传统回答三个基本问题：父亲是渔夫，儿子也当渔夫；猎物按部落惯例分配。变化很慢，今天只存在于少数偏远社区。AP 考试很少考，知道定义即可。

纯计划和纯市场都只是理论上的两端，现实中的经济都在中间，只是偏向不同

考点 KEY POINT

市场经济最本质的特征（defining characteristic）：private ownership of resources / protection of property rights。产权让人们有动力生产市场看重的东西。
市场经济靠 price system（价格机制） 配置资源：消费者愿意多付钱 → 价格上升 → 利润吸引企业多生产。资源自动流向价值更高的用途（Adam Smith 的 “invisible hand”）。
现实中几乎所有国家都是 mixed economy（混合经济）：以市场为主，政府负责提供公共物品、征税、保护产权、纠正市场失灵（Unit 6）。

没有人下命令，价格变化本身就把“大家想要什么”传递给了生产者——这就是 price system / invisible hand

故事 · 苏联漫画里的“钉子工厂” 一则流传很广的讽刺故事：计划部门按重量给钉子厂下指标，工厂就造出几根巨大、没人能用的钉子；改成按数量考核，工厂又造出成千上万根细得像针的小钉子。问题不在工人笨，而在于没有价格信号告诉工厂“人们真正需要什么”，工厂只对指标负责，不对消费者负责。

对比 · 市场怎么“知道”大家想要什么？某款奶茶突然在网上爆火，排队的人变多、价格上涨、利润变高 → 原来的店多开分店，别的品牌也推出同款。没有任何人下命令，资源就自动流向了消费者最想要的东西。这就是 price system 和 Adam Smith 说的 “invisible hand”。

Incentives Matter 激励很重要人会对激励（incentive）做出反应——这是经济学最基本的假设之一。

超市塑料袋从免费改成收费几毛钱，很多人开始自带购物袋。
外卖骑手按单计酬，所以会抢着多送单；如果改成固定月薪，送单速度往往会变慢。
上面的“钉子工厂”：工厂对考核指标做出反应，而不是对消费者的需要。

市场经济中，私有产权 + 利润给了人们生产“别人愿意买的东西”的激励；计划经济的难题之一，就是很难设计出同样有效的激励。

LAB 3市场还是计划？ · Market or Command?

判断每一句描述的是哪种经济体制。（得分：0 / ）

练习 Practice 1.2

以下为历年 AP 真题，点选项即时判分并显示解析。

1.2-12010 AP Micro Q2

The fundamental difference between a market economy and a command economy lies in which of the following?

Property rights and protection of private property
Absolute and comparative advantages
Specialization and trade
Taxes and subsidies
Positive and negative externalities

市场经济与计划经济最根本的区别是产权：市场经济保护私有产权，计划经济以公有为主。

1.2-22015 AP Micro 练习卷 Q17

Which of the following is necessary in a well-functioning capitalist economy but not in a command economy?

Centralized decision making
Scarcity of resources
Monopolies
Protection of property rights
Positive externalities

市场经济依靠私有产权提供激励，计划经济不需要（资源公有）。(A) 是计划经济的特征；(B) 稀缺性在所有经济中都存在。

1.2-32022 AP Micro 国际卷 Q4

A difference between command and market economic systems is that command economic systems

have a legal system that provides incentives to produce, whereas market economic systems do not
ensure efficiency, whereas market economic systems ensure equity
limit individual property rights, whereas market economic systems protect individual property rights
maximize producer and consumer surplus, whereas market economic systems do not
regulate production but not distribution, whereas market economic systems regulate both production and distribution

计划经济限制个人产权，市场经济保护个人产权。(A) 说反了；(B) 两种体制都不能“保证”效率或公平。

1.2-42023 AP Micro 国际卷 Q8

Which of the following is true in a command economy?

There is more private ownership of the factors of production than in a market economy.
Production decisions are based on the incentive of firms to maximize profits.
The government directs the use of factors of production.
The price system is used to allocate resources.
There is more freedom of enterprise than in a market economy.

计划经济由政府指挥生产要素的使用。(A)(B)(D)(E) 都是市场经济的特征。

1.2-52024 AP Micro Q2

Which of the following is consistent with a pure command economy?

Firms rely on the price system to allocate resources.
The government makes the major decisions concerning resource use.
Private individuals and firms own the productive resources.
Business owners determine how many workers to employ.
Entrepreneurs can make substantial economic profit.

纯计划经济：政府做主要的资源配置决策。其余选项都是市场经济的特征。

1.2-62025 AP Micro 国际卷 Q2

Which of the following best explains the difference in resource allocation between a pure command economy and a pure market economy?

A pure command economy allocates resources based on individual choices, whereas a pure market economy allocates resources using central planning.
A pure command economy allocates resources to maximize profits, whereas a pure market economy allocates resources to maximize revenues.
A pure command economy allocates resources using central planning, whereas a pure market economy relies on market forces to allocate resources.
A pure command economy allocates resources to eliminate income inequalities, whereas a pure market economy allocates resources to eliminate negative externalities.
A pure command economy allocates resources to achieve allocative efficiency, whereas a pure market economy allocates resources to achieve productive efficiency.

计划经济靠中央计划配置资源，市场经济靠市场力量（价格）。(A) 正好说反。

1.2-72019 AP Micro 练习卷 Q46

Individual private property rights provide people incentives to

meet societal goals rather than pursue their own self-interest
produce goods and services regardless of market demand
achieve equitable distribution of goods and services through competitive markets
focus only on benefits without regard to costs
produce goods and services that are valued in markets

有了产权，生产的收益归自己，人们就有动力生产市场上有人愿意买的东西。

1.3Production Possibilities Curve 生产可能性曲线

假设一个经济体只生产两种东西：机器人（Robots）和披萨（Pizza）。把所有资源都用上、用好，它最多能生产的各种组合连成的线，就是 PPC（production possibilities curve，也叫 PPF frontier）。PPC 把 Unit 1.1 的三个概念——稀缺、选择、机会成本——画在了一张图上。

定义 DEFINITION A PPC shows all the maximum combinations of two goods an economy can produce when it uses all of its resources fully and efficiently, given fixed resources and technology.
前提假设 Assumptions：① 只有两种商品 ② 资源数量与质量固定 ③ 技术固定 ④ 时间点固定

经济模型 Economic Models 现实世界太复杂，经济学家用 model（模型）把它简化：只保留最关键的几个变量，其余的先假设不变。这个“其他条件不变”的假设叫 ceteris paribus。PPC 就是 Unit 1 的第一个模型：现实中一个国家生产成千上万种商品，但我们只看两种，就能把“稀缺、取舍、机会成本、效率、增长”全部画在一张图上。

A 在曲线上 · B 在曲线内 · C 在曲线外

ON THE CURVE · A

Efficient 有效率（且可达）

资源被充分、有效利用，想多要一种就必须少要另一种。

INSIDE · B

Inefficient 无效率（可达）

有资源闲置（如失业）或资源浪费、配置不当。

OUTSIDE · C

Unattainable 目前达不到

以现有资源与技术无法生产。只有经济增长（PPC 外移）或贸易才能让消费到达这里。

考点 KEY POINT · 沿着曲线移动 = 取舍在曲线上从一点移到另一点（movement along the PPC），表示资源从一种商品重新配置（reallocate）到另一种商品，体现的是 trade-off 和机会成本。
从曲线内的点移到曲线上（如减少失业），可以两种商品同时增加，没有机会成本。

两种效率 Two Kinds of Efficiency Productive efficiency（生产效率）：曲线上的每一个点都是生产有效率的。
Allocative efficiency（配置效率）：曲线上只有某一个点是社会最想要的组合（生产的正是人们最看重的东西）。PPC 本身看不出是哪一点，需要知道社会偏好。

WORKED EXAMPLE 4荒岛求生：从数据画出 PPC 原创

Stranded on an island, Robin works 10 hours a day. In one hour she can catch 4 fish or gather 2 coconuts.

(a) Complete a production possibilities table and draw Robin's PPC with coconuts on the horizontal axis.
(b) What is Robin's opportunity cost of 1 coconut? Of 1 fish?
(c) Why is her PPC a straight line?

(a) 每多花 2 小时采椰子，就多 4 个椰子、少 8 条鱼：

Point	A	B	C	D	E	F
Hours on coconuts	0	2	4	6	8	10
Coconuts	0	4	8	12	16	20
Fish	40	32	24	16	8	0

每段都是“多 4 个椰子、少 8 条鱼”：斜率不变 → 机会成本不变（1 coconut = 2 fish）

(b) 1 小时 = 4 条鱼 = 2 个椰子，所以 1 coconut = 2 fish，1 fish = 1/2 coconut（互为倒数）。也可以直接用截距：40 ÷ 20 = 2。

(c) Robin 的每一小时在两种工作上的效率都一样，“资源”（她的时间）可以完美地在两种用途间转换，所以机会成本不变，PPC 是直线。

Shape 形状 = 机会成本的规律

PPC 的斜率（的绝对值）就是横轴商品的机会成本：多生产 1 单位横轴商品，要放弃多少单位纵轴商品。所以曲线的形状告诉你机会成本怎样变化。

Shape 形状	Opportunity cost 机会成本	Why 原因
Straight line 直线	Constant 不变	资源对两种商品同样适用（perfectly adaptable / substitutable）
Bowed out (concave to the origin) 外凸 — 最常见	Increasing 递增	资源是专用的（specialized, not perfectly adaptable）：先调用最适合的资源，越往后调用的资源越不适合，代价越来越大
Bowed in (convex to the origin) 内凹	Decreasing 递减	少见，考试偶尔作为干扰项出现

同样是“多 1 辆车”，越往右，曲线越陡，要放弃的小麦越多——斜率的绝对值就是机会成本

为什么机会成本会递增？假设一个国家把农田改去建工厂。第一批改的是最不适合种粮、最适合建厂的土地，少种的粮食很少；继续扩建工厂，就只能占用肥沃的良田，每多建一个工厂要少种的粮食越来越多。资源不能完美地从一种用途转到另一种用途（imperfect adaptability of resources），所以 PPC 外凸。

WORKED EXAMPLE 5期末周的 PPC：经济 vs 微积分原创

It is finals week and you have 10 hours left to study for two tests. The table shows the maximum combinations of extra points you can earn on your AP Micro test and your Calculus test.

Point	A	B	C	D	E	F
Micro points	0	10	20	30	40	50
Calculus points	30	28	24	18	10	0

(a) What is the opportunity cost of moving from C to D?
(b) You end up earning 20 Micro points and 20 Calculus points. Was your studying efficient?
(c) Can you earn 40 Micro points and 15 Calculus points?
(d) What is the total opportunity cost of moving from A to D?
(e) What does the pattern of opportunity costs tell you about the shape of your PPC? Why might it have this shape?
(f) A tutor shows you a much faster way to solve calculus problems, but nothing changes for Micro. How does your PPC change?

(a) 从 C (20, 24) 到 D (30, 18)：多拿 10 分经济，微积分从 24 降到 18，机会成本 = 6 Calculus points。

把表格画成图：(b) 的点在曲线内，(c) 的点在曲线外

(b) 拿 20 分经济时，微积分最多能拿 24 分，你只拿了 20 分 → 在 PPC 内，inefficient。说明有时间被浪费了（比如复习时一直刷手机）。

(c) 拿 40 分经济时，微积分最多 10 分，15 > 10 → 在 PPC 外，unattainable（以你现在的时间和效率做不到）。

(d) 微积分从 30 降到 18，共放弃 12 Calculus points（2 + 4 + 6）。

(e) 每多 10 分经济的机会成本依次是 2, 4, 6, 8, 10 分微积分——递增，所以 PPC 外凸（bowed out）。原因：最先挪给经济的，是微积分里收益最低的复习时间（早就会的题），而经济先拿的是最容易的分；越往后，挪走的越是微积分最需要的时间，换来的却是经济里最难拿的分。时间这种“资源”在两科之间不是完全可替代的。

(f) 只有微积分效率提高 → 微积分那一轴的截距外移（30 分以上），经济的截距仍是 50 分不变：PPC 只动一端（pivot）。

Shifts 曲线移动

PPC shifts OUTWARD 外移	PPC shifts INWARD 内移	PPC does NOT shift 不移动
• More resources 资源数量增加：labor force grows, immigration, new natural resources discovered • Better resources 质量提高：education, training (human capital) • Better technology 技术进步 • More physical capital 资本积累	• Natural disaster, war 自然灾害、战争 • Shrinking labor force 劳动力减少 • Loss of capital or natural resources 资本或自然资源损失	• Unemployment → 点移到曲线内，曲线不动 • Changes in prices or demand 价格、需求变化 • Changes in consumer tastes 偏好变化 • Reallocating resources → 沿着曲线移动

易错 TRAP

失业增加 ≠ PPC 内移。失业意味着已有的资源没用上，生产点跑到曲线内；PPC 代表的是“资源全用上时能生产多少”，资源总量没变，所以曲线不动。只有资源真的消失（灾害、移民外流）曲线才内移。
只改善一种商品的技术 → 只有这一种商品的截距外移（pivot）。另一种商品的最大产量不变。
价格、需求、偏好变化不会移动 PPC——PPC 只取决于资源和技术。

WORKED EXAMPLE 6六个事件，PPC 怎么变？原创

An economy produces only robots and pizza. For each event, decide whether the PPC shifts outward, shifts inward, pivots, or does not move.

大量年轻劳动力移民进来
一场洪水冲毁了农田和工厂
披萨烤炉技术突破（只影响披萨）
经济衰退，大批工人失业
消费者突然更爱吃披萨了
全国普及职业培训，工人技能提高

1. 大量年轻劳动力移民进来
劳动力（资源）增加 → 整条 PPC 外移。

2. 一场洪水冲毁了农田和工厂
资源真的消失了 → 整条 PPC 内移。

3. 披萨烤炉技术突破（只影响披萨）
只有披萨的最大产量增加 → 只有纵轴截距上移，机器人截距不变。

4. 经济衰退，大批工人失业
资源总量没变，只是闲置 → PPC 不动，生产点落到曲线内。

5. 消费者突然更爱吃披萨了
偏好不改变生产能力 → PPC 不动；市场会把资源转去做披萨，沿曲线移到披萨更多的点。

6. 全国普及职业培训，工人技能提高
人力资本（资源质量）提高 → 整条 PPC 外移。

判断口诀：先问“资源或技术变了吗？”——变了才移动曲线；没变（失业、偏好、价格）就只是点在动。

考点 KEY POINT · 资本品 vs 消费品如果一个国家今天把更多资源用来生产 capital goods（资本品，如机器、工厂），少生产 consumer goods（消费品），今天的生活水平会低一些，但未来 PPC 外移得更多（经济增长更快）。这是“今天的取舍影响明天的生产可能性”。

两国今天的 PPC 完全一样；A 把更多资源用来生产资本品，10 年后的生产能力明显更强

LAB 4PPC 互动实验 · Play with the PPC

① 形状：

拖动下方滑块沿曲线移动；点击图中任意位置放一个测试点，判断它在曲线上、曲线内还是曲线外

② 沿曲线移动： Robots = 0

③ 发生了什么？

点击一个事件，看 PPC 怎么变化。

练习 Practice 1.3

以下为历年 AP 真题，点选项即时判分并显示解析。

1.3-12015 AP Micro 练习卷 Q1

按原题重绘 · 1.3-1 与 1.3-2 共用此图

Given the production possibilities curve above, which of the following represents a movement from efficiency to inefficiency?

Point X to point W
Point X to point Z
Point Y to point Z
Point W to point Z
Point V to point Y

X 在曲线上（有效率），W 在曲线内（无效率），X → W 就是从有效率变为无效率。(B)(C) 沿曲线移动仍有效率；(D) 从无效率变为有效率；(E) V 在曲线外，目前达不到。

1.3-22015 AP Micro 练习卷 Q2

Based on a comparison of points X, Y, and Z, the opportunity cost of an additional consumer good is

highest at point X
highest at point Y
highest at point Z
lowest at point Y
the same at points X, Y, and Z

横轴商品（消费品）的机会成本 = 曲线斜率的绝对值。Z 点曲线最陡，多生产一单位消费品要放弃的资本品最多。

1.3-32023 AP Micro 国际卷 Q39

按原题重绘

The graph provided shows the production possibilities curve for a country’s economy. The economy is currently producing at point Z. What is the opportunity cost of changing production to point M?

3 units of Good Y
8 units of Good Y
3 units of Good X
4 units of Good X
2 units of Good X

从 Z (4, 4) 到 M (2, 7)：Y 增加 3，X 从 4 降到 2，放弃 2 units of Good X。机会成本是“放弃的东西”，不是“得到的东西”，所以不是 3 units of Y。

1.3-42025 AP Micro 国际卷 Q11

按原题重绘

The graph shows a production possibilities curve for a country.
Assuming no change in the country’s quantity and productivity of resources, the country can produce more capital goods without giving up any consumer goods if the country is currently producing at which point?

Point A
Point B
Point C
Point D
Point E

C 在曲线内（有闲置资源），可以直接多生产资本品而不减少消费品（C → B）。B、D、E 在曲线上，多要一种必须放弃另一种；A 在曲线外，达不到。

1.3-52021 AP Micro 国际卷 Q39

Combination	Houses	Grain (bushels)
A	0	1,000,000
B	1	950,000
C	2	850,000
D	3	700,000
E	4	400,000
F	5	0

The table above shows six possible combinations of houses and grain that a country can produce in a year using all currently available resources and technology. The opportunity cost of changing production from combination B to combination C is

1 house
2 houses
100,000 bushels of grain
850,000 bushels of grain
950,000 bushels of grain

从 B (1 house, 950,000) 到 C (2 houses, 850,000)：多造 1 栋房子，放弃 950,000 − 850,000 = 100,000 bushels of grain。机会成本用放弃的那种商品（粮食）表示。

1.3-62019 AP Micro 练习卷 Q2

Good X (units)	Good Y (units)
0	100
20	95
40	85
60	65
80	35
100	0

The table above shows the maximum possible output combinations of good X and good Y that Microland can produce by using all of its available resources and technology. As the production of good X increases, what happens to the opportunity cost of producing good X?

It decreases, because the production of good Y decreases by greater amounts.
It decreases, because the production of good Y increases by smaller amounts.
It remains constant, because the production of good X increases by the same amount.
It increases, because the production of good Y decreases by greater amounts.
It increases, because the production of good Y increases by smaller amounts.

X 每增加 20 单位，Y 依次减少 5、10、20、30、35，放弃的 Y 越来越多 → X 的机会成本递增（PPC 外凸）。(E) 错在“Y increases”——沿 PPC 增加 X 时 Y 是减少的。

1.3-72016 AP Micro 练习卷 Q17

A country produces computers and rice. If resources are fully employed and there is technological progress only in the production of rice, the opportunity costs of producing computers and rice will change in which of the following ways?

Opportunity cost of computers: Increase；Opportunity cost of rice: Increase
Opportunity cost of computers: Increase；Opportunity cost of rice: Decrease
Opportunity cost of computers: No change；Opportunity cost of rice: Decrease
Opportunity cost of computers: Decrease；Opportunity cost of rice: Increase
Opportunity cost of computers: Decrease；Opportunity cost of rice: Decrease

只有大米的技术进步：生产大米更容易，大米的机会成本下降；反过来，生产电脑要放弃的大米变多，电脑的机会成本上升。

1.3-82000 AP Micro Q46

按原题重绘

The diagram above shows an economy's current production possibilities curve for capital goods and consumer goods. If society chooses point B over point A, society is choosing

more future consumption in exchange for less current consumption
more current capital goods in exchange for less future consumption
more future and current consumption
less future consumption in exchange for more current consumption
less current capital goods in exchange for greater future consumption

B 点比 A 点生产更多资本品、更少消费品：今天少消费，换来更多机器厂房，未来 PPC 外移更多，未来能消费更多。

1.3-92022 AP Micro 国际卷 Q35

As an economy moves along its production possibilities curve, which of the following must be true?

The marginal benefit of the output is greater than the marginal cost of the output.
An increase in output results in a decrease in average total cost.
The marginal social cost of producing an additional output is zero.
Producing more of one good results in producing less of the other good.
The economy is producing the socially optimal combination of goods.

沿着 PPC 移动 = 资源在两种商品之间重新配置：多生产一种就必须少生产另一种。其余选项都与 PPC 无关或不一定成立。

1.3-102019 AP Micro 练习卷 Q16

A linear production possibilities curve indicates which of the following?

Constant opportunity costs
Decreasing opportunity costs
Increasing opportunity costs
Diminishing marginal returns
Labor-intensive production

直线 PPC 斜率不变 → 机会成本不变（资源对两种商品同样适用）。

1.4Comparative Advantage & Gains from Trade 比较优势与贸易利得

为什么一个各方面都更强的国家，仍然愿意和弱国做贸易？答案是 comparative advantage（比较优势）：决定该生产什么的不是“谁做得更多”，而是“谁做的代价更小”。

ABSOLUTE ADVANTAGE 绝对优势 Can produce more of a good with the same resources
— or the same amount using fewer resources.
比“谁做得多/谁用时少”

COMPARATIVE ADVANTAGE 比较优势 Can produce a good at a lower opportunity cost.
比“谁的机会成本低”——决定分工和贸易方向

梅西该不该自己剪草坪？假设梅西身体素质极好，剪完自家草坪只要 2 小时；邻居家的高中生 Leo 需要 4 小时。剪草坪这件事，梅西有绝对优势。
但梅西这 2 小时可以去拍一条运动品牌广告，赚 $20,000——这才是他剪草坪的机会成本。Leo 这 4 小时最好的选择是在咖啡店打工，赚 $60。
剪草坪的机会成本：梅西 $20,000，Leo $60 → Leo 有剪草坪的比较优势。梅西应该去拍广告，再花点钱请 Leo 剪草坪（比如 $100），两人都比自己干更划算。每个人专做自己机会成本最低的事，再交换——这就是专业化（specialization）和贸易的好处。

例子图 · 剪一次草坪，各自要放弃什么？

⚽

梅西：剪草坪要 2 小时；同样的 2 小时可以拍一条广告

机会成本 $20,000

🧑‍🎓

邻居 Leo：剪草坪要 4 小时；同样的 4 小时可以在咖啡店打工

机会成本 $60

🤝

结果：梅西有剪草坪的绝对优势（快一倍），Leo 有剪草坪的比较优势（代价低得多）。梅西付 Leo $100 请他剪：Leo 比打工多赚 $40，梅西多拍一条广告

双赢

机会成本的两种算法 · Output vs. Input

AP 题目里的表格有两种：给“产量”（同样资源能生产多少）或给“投入”（生产 1 单位要多少小时/资源）。公式正好相反，先看清是哪一种！

OUTPUT 产出型：表里是“能生产多少”

“Other goes Over” 对方商品放分子

OC of 1 X = Y 的产量X 的产量产量越大越有绝对优势。

INPUT 投入型：表里是“需要多少小时”

“It goes Over” 自己商品放分子

OC of 1 X = X 所需时间Y 所需时间用时越少越有绝对优势。

口诀记不住也没关系，按定义推：产出型里，“40 小麦或 20 电脑”说明 20 电脑 = 40 小麦，所以 1 电脑 = 2 小麦；投入型里，“玉米 2 小时、布 6 小时”说明 6 小时能做 1 布或 3 玉米，所以 1 布 = 3 玉米。

WORKED EXAMPLE 7产出型 Output Problem 原创

Using the same quantity of resources for one day, Atlantis can produce either 40 tons of wheat or 20 computers, and Borealis can produce either 30 tons of wheat or 10 computers.

	Wheat (tons)	Computers
Atlantis	40	20
Borealis	30	10

(a) Who has the absolute advantage in each good? (b) Who has the comparative advantage in each good? (c) Which terms of trade for computers would benefit both countries?

(a) Atlantis 两样都产得多（40 > 30，20 > 10）→ Atlantis 在两种商品上都有绝对优势。

(b) 先列机会成本表（产出型：对方放分子）：

	OC of 1 ton wheat	OC of 1 computer
Atlantis	20/40 = 0.5 computer	40/20 = 2 wheat ✓
Borealis	10/30 = 1/3 computer ✓	30/10 = 3 wheat

电脑：Atlantis 2 < Borealis 3 → Atlantis 有电脑的比较优势；小麦：Borealis 1/3 < Atlantis 0.5 → Borealis 有小麦的比较优势。

画在同一张图上：斜率的绝对值 = 横轴商品（电脑）的机会成本。Atlantis 的线更平 → 电脑的机会成本更低

(c) 互利的贸易条件必须在两国机会成本之间：1 computer 换 2 到 3 tons of wheat 之间（例如 2.5）。Atlantis 出口电脑，每台换回 2.5 吨，比自己生产时放弃的 2 吨多；Borealis 用 2.5 吨换 1 台电脑，比自己造一台要放弃的 3 吨少。

WORKED EXAMPLE 8投入型 Input Problem 原创

The table shows the number of labor hours needed to produce one unit of each good.

	Corn (1 bushel)	Cloth (1 yard)
Mexland	2 hours	6 hours
Norland	3 hours	4 hours

Identify the absolute and comparative advantages, and the good each country should specialize in.

绝对优势（看谁用时少）：玉米 Mexland 2 < 3；布 Norland 4 < 6。各有一项。

机会成本（投入型：自己放分子）：

	OC of 1 corn	OC of 1 cloth
Mexland	2/6 = 1/3 cloth ✓	6/2 = 3 corn
Norland	3/4 = 0.75 cloth	4/3 ≈ 1.33 corn ✓

答：Mexland 有玉米的比较优势，应专门生产玉米；Norland 有布的比较优势，应专门生产布。互利的贸易条件：1 yard of cloth 换 4/3 到 3 bushels of corn 之间。

WORKED EXAMPLE 9专业化让两国的“总蛋糕”变大原创

Continue the Mexland–Norland example. Each country has 12 labor hours. Mexland can therefore produce 6 bushels of corn or 2 yards of cloth; Norland can produce 4 bushels of corn or 3 yards of cloth.

(a) Without trade, each country spends half its hours on each good. What is total output?
(b) If each country specializes according to comparative advantage, what is total output?
(c) They trade 3 bushels of corn for 1.5 yards of cloth. Show that both countries consume more than without trade.

	(a) 不贸易：各用 6 小时	(b) 专业化	(c) 贸易后消费
Mexland	3 corn + 1 cloth	6 corn（全做玉米）	6 − 3 = 3 corn + 1.5 cloth
Norland	2 corn + 1.5 cloth	3 cloth（全做布）	3 − 1.5 = 1.5 cloth + 3 corn
Total	5 corn + 2.5 cloth	6 corn + 3 cloth	6 corn + 3 cloth

资源和技术都没变，只是分工方式变了，两种商品的总产量都增加

(c) Mexland：3 corn + 1.5 cloth，比不贸易时（3 + 1）多 0.5 码布；Norland：3 corn + 1.5 cloth，比不贸易时（2 + 1.5）多 1 蒲式耳玉米。两国都超出了自己的 PPC。

贸易条件 3 corn = 1.5 cloth，即 1 cloth = 2 corn，落在两国布的机会成本（Norland 4/3 corn，Mexland 3 corn）之间，所以双方都获益。

考点 KEY POINT · 比较优势的三条铁律

两个国家、两种商品时，一个国家不可能在两种商品上都有比较优势（两种机会成本互为倒数）。但它可以在两种商品上都有绝对优势。
只要两国的机会成本不同，就存在互利贸易；如果机会成本完全相同，就没有比较优势，专业化和贸易没有好处。
分工和贸易方向只看比较优势，不看绝对优势。

Terms of Trade 贸易条件与贸易利得

Terms of trade 是两种商品交换的比率。只有当它落在两国机会成本之间时，双方才都获益。等于某一国的机会成本时，那个国家没得到好处（也没损失）；落在区间外，就有一国受损，不会自愿交易。

蓝线：Atlantis 的 PPC；绿虚线：按 1 电脑 = 2.5 吨小麦贸易后的消费可能性

接例题 7：Atlantis 专门生产 20 台电脑，按 1 : 2.5 用其中 8 台换 20 吨小麦，最后消费 12 台电脑 + 20 吨小麦。

如果不贸易、自己生产 12 台电脑，Atlantis 最多只有 40 − 2×12 = 16 吨小麦。

结论专业化 + 贸易让一国的消费点超出自己的 PPC（但生产点仍在 PPC 上）。这就是 gains from trade。

LAB 5比较优势计算器 · Comparative Advantage Calculator

题型：

载入例题：

试一个贸易条件： 1 Computers 换 Wheat

练习 Practice 1.4

以下为历年 AP 真题，点选项即时判分并显示解析。

1.4-12013 AP Micro Q46

Suppose that in one week Sam can knit 5 sweaters or make 4 blankets and Rob can knit 10 sweaters or make 6 blankets. Which of the following is true?

Sam has an absolute advantage in making blankets.
Sam has an absolute advantage in knitting sweaters.
Sam has a comparative advantage in making blankets.
Sam has a comparative advantage in knitting sweaters.
Sam has neither a comparative nor an absolute advantage in knitting sweaters or making blankets.

产出型（对方放分子）。1 条毯子的机会成本：Sam = 5/4 = 1.25 件毛衣，Rob = 10/6 ≈ 1.67 件 → Sam 有毯子的比较优势。Rob 两样都做得多，Sam 没有任何绝对优势。

1.4-22014 AP Micro 练习卷 Q47

Using the same amount of time and resources, Jack can assemble either 10 bikes or 5 computers, whereas Sam can assemble either 5 bikes or 5 computers. Based on the data, which of the following statements is correct?

Sam has an absolute advantage in assembling bikes.
Sam has an absolute advantage in assembling computers.
Sam has a comparative advantage in assembling bikes.
Jack has a comparative advantage in assembling bikes.
Jack has a comparative advantage in assembling both bikes and computers.

1 辆自行车的机会成本：Jack = 5/10 = 0.5 台电脑，Sam = 5/5 = 1 台 → Jack 有自行车的比较优势；Sam 有电脑的比较优势。电脑两人都是 5 台，谁都没有绝对优势。

1.4-32016 AP Micro 练习卷 Q46

Dana and Robin produce smoothies and pizza. In one hour Dana can make 20 smoothies or 10 pizzas. In one hour Robin can make 18 smoothies or 6 pizzas. Which of the following statements is true?

Robin has an absolute advantage in making smoothies and a comparative advantage in making pizzas.
Robin has both an absolute advantage and a comparative advantage in making pizzas.
Dana has a comparative advantage in making both smoothies and pizzas.
Dana has a comparative advantage in making pizzas, and Robin has a comparative advantage in making smoothies.
Dana has a comparative advantage in making smoothies, and Robin has a comparative advantage in making pizzas.

1 个披萨的机会成本：Dana = 20/10 = 2 杯，Robin = 18/6 = 3 杯 → Dana 有披萨的比较优势。1 杯奶昔：Dana = 0.5 个披萨，Robin = 1/3 个 → Robin 有奶昔的比较优势。Dana 两样都有绝对优势。

1.4-42018 AP Micro 练习卷 Q32

Both Amy and Brad produce and consume apple pie and ice cream. In one hour, Brad makes five apple pies or ten gallons of ice cream while Amy makes fifteen apple pies or fifteen gallons of ice cream. Based on the above information, one can correctly conclude that

Brad has an absolute advantage in making ice cream and will sell ice cream to Amy
Brad has a comparative advantage in making ice cream and will sell ice cream to Amy
Brad does not have a comparative advantage in making either good and will not trade with Amy
Brad has an absolute advantage in making apple pies but a comparative advantage in making ice cream
Brad’s opportunity cost of making ice cream is higher than Amy’s

1 gallon 冰淇淋的机会成本：Brad = 5/10 = 0.5 个派，Amy = 15/15 = 1 个派 → Brad 有冰淇淋的比较优势，会把冰淇淋卖给 Amy。Amy 两样都有绝对优势。

1.4-52022 AP Micro 国际卷 Q5

Dr. Art and Dr. Zed jointly own an outpatient surgery practice. Dr. Art takes 2 hours to perform knee surgery and 1 hour to perform elbow surgery. Dr. Zed takes 4 hours to perform knee surgery and 1 hour to perform elbow surgery. Which of the following conclusions is supported by the information provided?

Dr. Art has a comparative advantage in elbow surgery.
Dr. Zed has a comparative advantage in elbow surgery.
Dr. Zed does not have a comparative advantage in performing either procedure.
Dr. Art does not have a comparative advantage in performing either procedure.
Dr. Zed has an absolute advantage in performing both procedures.

投入型（自己放分子）。1 台肘部手术的机会成本：Art = 1/2 台膝部手术，Zed = 1/4 台 → Zed 有肘部手术的比较优势；Art 有膝部手术的比较优势（2/1 = 2 < 4/1 = 4）。肘部手术两人用时相同，Art 只有膝部手术的绝对优势。

1.4-62025 AP Micro 国际卷 Q52

	Smartphone	Cake
Alpha	5 hours	2 hours
Beta	2 hours	1 hour

The table shows the number of labor hours it takes Alpha and Beta to produce a smartphone or a cake with the same resources.
If tasks are assigned according to comparative advantage, which of the following is true?

Alpha will produce both goods.
Beta will produce both goods.
Alpha will produce smartphones and Beta will produce cakes.
Alpha will produce cakes and Beta will produce smartphones.
Alpha has an absolute advantage in producing both goods.

投入型。1 部手机的机会成本：Alpha = 5/2 = 2.5 个蛋糕，Beta = 2/1 = 2 个 → Beta 有手机的比较优势；Alpha 有蛋糕的比较优势（0.4 < 0.5）。Beta 两样都用时更少，有两项绝对优势（E 说反了）。

1.4-72023 AP Micro 国际卷 Q49

	Orange juice (liters)	Canvases
Stefan	40	30
Donna	20	10

Stefan and Donna produce orange juice and canvases. The table provided shows the maximum possible production of orange juice OR canvases that can be produced by Stefan and Donna. Which of the following terms of trade would be mutually beneficial to Stefan and Donna?

1 canvas for 0.4 liter of orange juice
1 canvas for 0.5 liter of orange juice
1 canvas for 1 liter of orange juice
1 canvas for 1.5 liters of orange juice
1 canvas for 2.5 liters of orange juice

1 canvas 的机会成本：Stefan = 40/30 ≈ 1.33 liters，Donna = 20/10 = 2 liters。贸易条件须在 1.33 和 2 之间 → 1.5 liters。

1.4-82025 AP Micro 国际卷 Q4

Ming and Andreas are the only two employees at a pizza shop where they can either make pizzas or take orders. Ming has a comparative advantage over Andreas in making pizzas. Which of the following statements must be true?

Ming has a higher opportunity cost for making pizzas.
Ming has an absolute advantage in making pizzas.
There is no advantage in specialization for Andreas.
Andreas has an absolute advantage in taking orders.
Andreas has a lower opportunity cost for taking orders.

Ming 在做披萨上有比较优势，等价于 Andreas 在接单上的机会成本更低（两种机会成本互为倒数）。比较优势推不出任何绝对优势（B、D 不一定成立）。

1.4-92000 AP Micro Q17

A country can consume beyond its present production possibilities curve when it

trades with other countries, thus taking advantage of different opportunity costs
reduces unemployment, thus increasing output
experiences decreasing opportunity costs
faces an upward-sloping production possibilities curve
faces a downward-sloping production possibilities curve

贸易让各国按比较优势分工、利用机会成本的差异，消费点可以超出自己的 PPC。(B) 减少失业只能让生产点回到 PPC 上，不能超出。

1.5Cost-Benefit Analysis 成本收益分析

经济学假设人是 rational（理性的）：在做选择时会比较收益和成本，追求自身利益（self-interest）。理性不等于自私或冷血，而是“按自己的目标，选净收益最大的方案”。

定义 DEFINITION Net Benefit = Total Benefit − Total Cost A rational decision maker chooses the option (or quantity) that maximizes net benefit — not the one that maximizes total benefit, and not the one that minimizes total cost.

考纲细节 · 收益和成本分别指什么（CED CBA-1.A）

Benefit 收益：对消费者，总收益就是 utility（效用，满足感）；对企业，总收益就是 total revenue（总收入），企业追求的是利润。
Cost 成本：经济学里所有成本都是机会成本——既包括真的付出去的钱（explicit），也包括放弃的机会（implicit）。理性的人两种都要算。

Explicit vs. Implicit Costs 显性成本与隐性成本

EXPLICIT COST 显性成本

真的掏了钱

Out-of-pocket payments：房租、工资、原材料、学费。

IMPLICIT COST 隐性成本

没掏钱，但放弃了机会

The value of forgone opportunities：放弃的工资、自己房子本可收的租金、自己的钱本可赚的利息。

经济成本 = 显性 + 隐性（Unit 3.4 会再用到） Accounting profit = Total revenue − Explicit costs
Economic profit = Total revenue − Explicit costs − Implicit costs
经济学家看的是 economic profit：只有它 ≥ 0，这个选择才真的值得。

WORKED EXAMPLE 10辞职去当全职主播，值不值？原创

Mia quits her job paying $50,000 a year to become a full-time streamer. In her first year, subscriptions, ads, and sponsorships bring in total revenue of $120,000. She pays $60,000 for equipment, studio rent, and a part-time video editor. Calculate her accounting profit and economic profit. Was quitting a good decision?

会计利润 = 120,000 − 60,000 = $60,000。

经济利润 = 120,000 − 60,000 − 50,000（放弃的工资，隐性成本）= $10,000。

单位：千美元。三根条一样长（都是 $120k 的收入），区别在于“成本”算没算上放弃的工资

结论：经济利润 > 0，做主播比上班多赚 $10,000，是好决定。如果第二年收入降到 $100,000（成本不变），会计利润仍有 $40,000，看起来“赚钱”，但经济利润是 −$10,000——她不如回去上班。

WORKED EXAMPLE 11暑假三选一：只能比较总量的决策原创

Kevin can choose only one plan for the summer. The table shows the total benefit and the explicit cost of each plan.

Plan	Total benefit	Explicit cost
💼 Internship 实习	$3,000 pay + $2,000 value of experience	$400 commuting
🏫 Summer school 夏校	$6,000 value of courses	$4,000 tuition
☕ Café job 咖啡店打工	$4,000 pay	$200 uniform and commuting

(a) Which plan should a rational Kevin choose? (b) What is the opportunity cost of that choice? (c) Why can't Kevin use marginal analysis here?

(a) 净收益：实习 5,000 − 400 = $4,600；夏校 6,000 − 4,000 = $2,000；打工 4,000 − 200 = $3,800。选实习。

(b) 机会成本 = 次优选择的价值 = 打工的净收益 $3,800。选实习“多赚”的是 4,600 − 3,800 = $800 > 0，说明这个选择真的值得。

(c) 这是“三选一”的决定，没办法“多实习一点点、少打工一点点”。CED 明确指出：有些决策可以拆成一个个单位用边际分析（MB vs MC），有些决策不能拆分，只能比较各方案的总收益与总成本（CBA-1.B.2）。

LAB 6找到最优数量 · Total Approach

你开了一家奶茶店，正在决定每晚 6 点以后再多营业几个小时。越晚客人越少（多营业一小时带来的收益越来越少），而深夜员工要付加班费（多营业一小时的成本越来越高）。表格是营业不同小时数的总收益和总成本。先自己算出每一行的净收益，再点击你认为最优的那一行。

Extra hours	Total Benefit ($)	Total Cost ($)	Net Benefit ($)	MB ($)	MC ($)

点击表格中的一行作答。

净收益 = TB 与 TC 之间的竖直距离。3 小时时距离最大；到 6 小时 TC 已经超过 TB

练习 Practice 1.5

以下为历年 AP 真题，点选项即时判分并显示解析。

1.5-12024 AP Micro Q9

Number of scarves	Total cost ($)	Total benefit ($)
1	8	17
2	19	33
3	33	48
4	49	62
5	85	69

Lily knits scarves for her business. The table provided outlines Lily's daily total cost and total benefit of knitting scarves. How many scarves should Lily knit each day to maximize her total net benefit?

净收益 = TB − TC：9, 14, 15, 13, −16，3 条围巾时最大。边际法：第 3 条 MB 15 > MC 14，第 4 条 MB 14 < MC 16。

1.5-22021 AP Micro 国际卷 Q15

Hours at the library	Total benefit	Total cost
1	12	10
2	20	13
3	26	18
4	31	25
5	33	33
6	35	42

The table provided shows the total benefits and costs of studying at the library. If the student is rational, the optimal number of hours to spend at the library is

净收益：2, 7, 8, 6, 0, −7，3 小时最大。边际法：第 3 小时 MB 6 > MC 5，第 4 小时 MB 5 < MC 7。

1.5-32010 AP Micro Q16

Carlos has a van with 20 seats and charges $10 per person per ride to the airport from downtown. Carlos' cost of the trip is $140 for any number of passengers. On one trip, Carlos has 19 seats filled when a person offers him $5 for the last seat. Should Carlos accept the offer?

No, since the $5 fare offered is below his average cost of $7.
No, since the average variable cost is greater than $5.
No, since it is illegal to charge different prices for the same service.
Yes, since the marginal benefit exceeds the marginal cost.
Yes, since his total revenue exceeds his total cost by $5.

多载 1 个人的边际成本是 0（行程成本 $140 不随人数变化），边际收益是 $5，MB > MC → 应该接受。(A)(B) 用平均成本做决策，是典型错误。

1.5-42018 AP Micro 练习卷 Q2

Quantity of pollution reduction (tons)	Total benefit ($)
0	0
1	300
2	550
3	650
4	725
5	775

The table above shows the total benefit associated with reducing different levels of pollution on a small island. The cost of eliminating one ton of pollution is $150. Which of the following is the optimal quantity of pollution to eliminate?

5 tons
4 tons
3 tons
2 tons
1 tons

每多减少 1 吨污染的边际收益：300, 250, 100, 75, 50，边际成本恒为 $150。第 2 吨 MB 250 > 150，第 3 吨 MB 100 < 150 → 减少 2 吨。

1.5-52012 AP Micro Q28

Instead of being employed at a printing company at a salary of $25,000 per year, Sally starts her own printing firm. Rather than renting a building that she owns to someone else for $10,000 per year, she uses it as the location for her company. Her costs for workers, materials, advertising, and energy during her first year are $125,000. If the total revenue from her printing company is $155,000, her total economic profit is

-$5,000
$5,000
$20,000
$30,000
$120,000

经济利润 = 总收益 − 显性成本 − 隐性成本 = 155,000 − 125,000 − 25,000（放弃的工资）− 10,000（放弃的租金）= −$5,000。会计利润是 $30,000（D）。

1.6Marginal Analysis & Consumer Choice 边际分析与消费者选择

1.5 是把每个方案的“总量”都算出来再比较。实际做决定时，人们更常问的是：“再多做一个，值不值？” 这就是 marginal analysis（边际分析）。“Marginal” 在经济学里一律翻译成“额外的、多一个的”。

Term	Meaning	Formula
Marginal Benefit (MB) 边际收益	多一单位带来的额外收益；对消费者 = 愿意为多一单位支付的最高价格	MB = ΔTB / ΔQ
Marginal Cost (MC) 边际成本	多一单位带来的额外成本；对生产者 = 愿意接受的最低价格	MC = ΔTC / ΔQ
Marginal Utility (MU) 边际效用	多消费一单位带来的额外满足感（utility，单位叫 util）	MU = ΔTU / ΔQ

The MB = MC Rule 最优决策规则

规则 RULE

MB > MC → 多做这一单位能增加净收益 → do more
MB < MC → 这一单位让净收益减少 → do less
MB = MC → 净收益已经最大 → optimal quantity

表格题里如果没有恰好相等的那一单位：做到“最后一个 MB ≥ MC 的单位”为止。

绿色面积 = 做到 Q* 为止累积的净收益；超过 Q* 后每一单位都在“倒贴”（红色）。所以最优数量在 MB 与 MC 相交处

LAB 7一次只想一个 · Think at the Margin

晚上 11 点，你在追一部新剧。每多看一集，带来的快乐越来越少（MB = $5, $4, $3, $2, $1，代表你愿意为这一集付的钱），而熬夜的代价越来越大——明天上课更困、作业写不完（MC = $1, $2, $3, $4, $5）。点“考虑下一集”，每次只判断一集。

还没有开始。

易错 TRAP · 沉没成本 Sunk Cost 已经花掉、怎样都收不回来的钱叫 sunk cost。它不会因为你现在的选择而改变，所以不应该影响边际决策。例如：电影票 $15 已经付了且不能退，看了半小时发现很难看——是否继续看，只取决于“接下来 1.5 小时的收益 vs 成本”，和那 $15 无关。

考纲细节 · 最优数量与固定成本无关（CED CBA-2.B.2）最优数量不取决于已经确定的固定成本（或固定收益），包括沉没成本。原因很简单：不管你多做还是少做，这些成本都一样，它们不会改变“下一单位”的 MB 和 MC。

WORKED EXAMPLE 12网约车司机：要不要再接最后一单？原创

Dan drives for a ride-hailing app. Each month he pays $800 for his car loan and $200 for insurance, whether he drives or not. At 10 p.m. he gets one more request: the fare is $25. The trip will use $6 of gas, and Dan values the extra 40 minutes of his time at $12. Should he accept?

MB = 这一单的车费 $25。

MC = 只因为这一单才多出来的成本 = 油费 $6 + 时间的机会成本 $12 = $18。

结论：MB $25 > MC $18 → 接单，净收益增加 $7。车贷和保险共 $1,000 是固定成本，接不接这一单都要付，不影响决策。把它们“平摊”到每一单上去比较，是常见错误（真题 2010 Q16 Carlos 的面包车就是这个考法）。

Diminishing Marginal Utility 边际效用递减

Cups of bubble tea	Total utility	Marginal utility
0	0	—
1	5	5
2	9	4
3	12	3
4	14	2
5	15	1
6	15	0
7	14	−1

大热天的第一杯奶茶最幸福，第二杯还不错，到第五杯已经喝不下了：每多一杯带来的额外满足感越来越少，这就是 law of diminishing marginal utility。这也解释了为什么“第二杯半价”能促销——商家知道你对第二杯的评价更低。

MU > 0 时，TU 仍在增加，只是增加得越来越慢。
MU = 0 时，TU 达到最大。
MU < 0 时（喝到难受），TU 开始下降。
TU = 前面所有 MU 之和：5 + 4 + 3 + 2 + 1 = 15。

上：总效用先升后平再降；下：边际效用一路递减。MU 为正 → TU 上升；MU = 0 → TU 最大；MU 为负 → TU 下降

补充 · 边际效用一定从第一单位就开始递减吗？不一定。比如集卡：凑齐整套之前，最后几张卡的边际效用可能反而更高；学钢琴，前几节课很枯燥，会弹曲子以后越来越有乐趣。教材称之为 “the occasional ups and downs of marginal utility”。但 AP 考题默认边际效用递减，答题时按递减处理。

WORKED EXAMPLE 13钻石与水的悖论 Diamond–Water Paradox 原创

💧

水：没有它活不下去（总效用极高），但一瓶矿泉水只要几块钱

💎

钻石：没有它完全不影响生活（总效用低），却要几万块

Use marginal utility to explain why people pay far more for a diamond than for a bottle of water.

人们愿意为“多一单位”支付的价格取决于边际效用，而不是总效用。

水非常充足，我们已经消费了很多，再多一瓶的边际效用很低；钻石非常稀少，多一颗的边际效用很高。所以 MU_water < MU_diamond，价格也一样。

真题对应：2012 AP Micro Q49（见练习 1.6-2）。

Budget Constraint 预算约束

消费者想要最大化效用，但受到收入和价格的限制（CED CBA-2.A.1：consumers face constraints）。在两种商品的情况下，所有“正好花完钱”的组合连成一条线，叫 budget line（预算线）。

公式 FORMULA P_X · X + P_Y · Y = Income 线上：正好花完；线内：买得起但有钱没花完；线外：买不起。

LAB 8 的预算线：浅蓝色区域内的组合都买得起；效用最大的组合一定在线上（钱要花完）

WORKED EXAMPLE 14画预算线原创

Mei has $12 to spend on comic books ($4 each) and snacks ($2 each). (a) What are the two intercepts of her budget line? (b) If she buys 2 comic books, how many snacks can she buy? (c) What is the opportunity cost of 1 comic book?

(a) 全买漫画：12 ÷ 4 = 3 本；全买零食：12 ÷ 2 = 6 份。

(b) 2 本漫画花 $8，剩 $4，可买 2 份零食。

(c) 1 本漫画（$4）= 2 份零食（$2 × 2），机会成本是 2 snacks。预算线其实就是消费者的“PPC”：它也是一条取舍线。

考纲边界无差异曲线（indifference curves）不考；但“比较 MU/P”在考试范围内（CED Exclusion Statement）。

Utility-Maximizing Rule 效用最大化法则

消费者的钱是有限的（budget constraint），两种商品价格又不同，那么最后一块钱该花在哪里？答案是比较“每一块钱能买到的边际效用”：MU / P。

法则 RULE MU_XP_X = MU_YP_Y and all income is spent 如果 MU_X/P_X > MU_Y/P_Y：花在 X 上的每一块钱更“值”，应多买 X、少买 Y。多买 X 后 MU_X 递减，少买 Y 后 MU_Y 上升，两个比值逐渐相等。

WORKED EXAMPLE 15该多买哪个？原创

Kim spends all of her income on books and movie tickets. A book costs $3 and a movie ticket costs $4. For the last book she bought, MU = 60 utils; for the last movie ticket, MU = 40 utils. Is Kim maximizing utility? If not, what should she do?

MU_book/P_book = 60/3 = 20 utils per dollar；MU_movie/P_movie = 40/4 = 10 utils per dollar。

20 ≠ 10，没有最大化。花在书上的每一块钱更值 → 多买书、少买电影票，直到两个比值相等。

易错：不能只比较 MU（60 vs 40），一定要先除以价格。

LAB 8效用最大化购物实验 · Spend $10 Wisely

放学后你有 $10 零花钱。奶茶 Bubble tea $2 一杯，炸鸡块 Nuggets $1 一份。表格是每多买一个带来的边际效用。用 + / − 调整数量，找到总效用最大的组合。

BUBBLE TEA · $2

NUGGETS · $1

已花 $0 / $10 · 总效用 0 utils

提示：每一块钱都应该花在“每元边际效用”最高的地方。

练习 Practice 1.6

以下为历年 AP 真题（最后一题为原创补充），点选项即时判分并显示解析。

1.6-12005 AP Micro Q7

In a given time period, a person consumes more and more of a good or service and, as a result, enjoys each additional unit less and is willing to pay less for each additional unit. This behavior is consistent with the law of

diminishing returns
diminishing marginal product
diminishing marginal utility
increasing costs
scarce resources

每多消费一单位，额外的满足感（边际效用）越来越少 → 边际效用递减。(A)(B) 是生产理论（Unit 3）的概念。

1.6-22012 AP Micro Q49

At her current level of consumption, a consumer is willing to pay up to $1.50 for a bottle of water and up to $1,500 for a diamond ring because the

total utility of diamond rings is greater than the total utility of water
total utility of water is less than the marginal utility of a diamond ring
marginal utility of a bottle of water is less than the marginal utility of a diamond ring
marginal utility of a bottle of water is greater than the marginal utility of a diamond ring
consumer is irrational and does not understand that water is more important than a diamond

愿意为“多一单位”付多少，取决于边际效用，而不是总效用。水很多，最后一瓶水的边际效用很低；钻石很少，边际效用很高（diamond-water paradox）。

1.6-32013 AP Micro Q53

If a good is available free of charge, an individual will consume it until

marginal utility is zero
average utility is zero
total utility is zero
marginal utility equals average utility
marginal utility equals total utility

免费意味着价格为 0，只要多消费一单位还有正的边际效用就会继续，直到 MU = 0（此时总效用最大）。

1.6-42024 AP Micro Q5

Number of salads	Marginal utility
1	15
2	11
3	3
4	1
5	-3

During the week, Juliette can eat salads for lunch. Based on the provided table, how many salads consumed per week would maximize Juliette's total utility?

不考虑价格时，只要 MU > 0 就继续消费。第 4 份 MU = 1 > 0，第 5 份 MU = −3 < 0 → 4 份时总效用最大。

1.6-52014 AP Micro 练习卷 Q52

Garcia is currently spending his entire lunch budget on 3 sodas and 4 hot dogs. At his current level of consumption, Garcia’s marginal utility for sodas is 5 utils and his marginal utility for hot dogs is 10 utils. In order to maximize his total utility, Garcia should

consume more sodas and fewer hot dogs regardless of the prices
consume more hot dogs and fewer sodas regardless of the prices
maintain his current level of consumption of sodas and hot dogs regardless of the prices
maintain his current level of consumption if the price of a soda is $1 and the price of a hot dog is $2
maintain his current level of consumption if the price of a soda is $2 and the price of a hot dog is $1

最大化条件 MU/P 相等：如果汽水 $1、热狗 $2，则 5/1 = 10/2 = 5，已经最优。(E) 的价格下 5/2 ≠ 10/1。(A)(B)(C) 都忽略了价格。

1.6-62015 AP Micro 练习卷 Q49

Oscar spent his entire income on only two goods: good X and good Y. At his current consumption of the two goods, the marginal utility of X is 8 and the marginal utility of Y is 2. If the price of X is $4.00 and the price of Y is $0.50, then to maximize his total utility, Oscar should have

bought more X and more Y
bought more X and less Y
bought less X and more Y
bought less X and less Y
maintained his current consumption

MU/P：X = 8/4 = 2，Y = 2/0.5 = 4。Y 每元效用更高 → 少买 X、多买 Y。

1.6-72016 AP Micro 练习卷 Q50

Assume Pat spends all of her allowance to purchase 4 apples and 4 candy bars. Pat’s marginal utility of the fourth apple is 20 utils, and her marginal utility of the fourth candy bar is 40 utils. If an apple costs $1.00 and a candy bar $0.50, to maximize utility Pat should

purchase more apples and more candy bars
maintain the current purchase of 4 apples and 4 candy bars
purchase more apples and fewer candy bars
purchase fewer apples and more candy bars
purchase fewer apples and fewer candy bars

MU/P：苹果 = 20/1 = 20，糖果 = 40/0.5 = 80。糖果每元效用更高 → 少买苹果、多买糖果。

1.6-82018 AP Micro 练习卷 Q50

Mickey has a $20 gift card that she is planning to use to download 10 songs and 5 games. The download price for each song is $1 and the download price for each game is $2. Her marginal utility from the tenth song is 30, and her marginal utility from the fifth game is 70. Based on this information, which of the following statements is true?

Mickey’s plan will maximize her utility.
Mickey can increase utility by buying more songs and fewer games.
Mickey can increase utility by buying more games and fewer songs.
Since games are twice as expensive as songs, Mickey should buy twice as many songs.
Since games are twice as expensive as songs, Mickey should buy twice as many games.

MU/P：歌曲 = 30/1 = 30，游戏 = 70/2 = 35。游戏每元效用更高 → 多买游戏、少买歌曲。(D)(E) 数量比例与最优条件无关。

1.6-92019 AP Micro 练习卷 Q35

	Video games	Comic books
Price per unit	$25	$10
Marginal utility	50	50

The table below shows the per-unit prices and marginal utility for the last unit of video games and comic books that Kyle purchased.
Kyle spent all of his allocated budget on video games and comic books. To maximize his utility, Kyle should have purchased

more video games and fewer comic books
fewer video games and more comic books
fewer of both goods
equal amounts of both goods
more of both goods

MU/P：游戏 = 50/25 = 2，漫画 = 50/10 = 5。漫画每元效用更高 → 少买游戏、多买漫画。MU 相等不代表最优，要除以价格。

1.6-102010 AP Micro Q20

Units of pizza	MU of pizza	Units of pens	MU of pens
1	20	1	8
2	18	2	7
3	16	3	6
4	14	4	5
5	12	5	4
6	10	6	3
7	9	7	2
8	8	8	1

The student has $10 and spends it all on pizza and pens. If the price of a unit of pizza is $2 and the price of a unit of pens is $1, the student will maximize utility by purchasing which of the following combinations of pizzas and pens?

Pizzas: 5；Pens: 3
Pizzas: 4；Pens: 2
Pizzas: 3；Pens: 4
Pizzas: 3；Pens: 1
Pizzas: 2；Pens: 6

先算 MU/P：披萨（$2）20/2 = 10, 9, 8, 7, 6…；笔（$1）8, 7, 6, 5…。4 个披萨 + 2 支笔正好花 $10，最后一个披萨 14/2 = 7 = 最后一支笔 7/1 → 最优。(A) 要 $13，超出预算。

1.6-112025 AP Micro 国际卷 Q31

Quantity of chocolate bars	MU of chocolate bars (utils)	Quantity of pizza slices	MU of pizza slices (utils)
1	10	1	26
2	6	2	20
3	5	3	15
4	4	4	12
5	2	5	10
6	1	6	9

The table shows the marginal utility that Olivia derives from consuming two goods: chocolate bars and slices of pizza.
Olivia has a limited weekly income of $10 and spends it all on chocolate bars and slices of pizza. Assume the price of each chocolate bar is $1 and the price of each slice of pizza is $2. What combination of chocolate bars and pizza slices will maximize Olivia’s total utility given her weekly income?

0 chocolate bars and 5 slices of pizza
1 chocolate bar and 2 slices of pizza
2 chocolate bars and 4 slices of pizza
4 chocolate bars and 3 slices of pizza
6 chocolate bars and 2 slices of pizza

MU/P：巧克力（$1）10, 6, 5, 4, 2, 1；披萨（$2）13, 10, 7.5, 6, 5, 4.5。2 块巧克力 + 4 片披萨正好花 $10，最后一块巧克力 6 = 最后一片披萨 12/2 = 6 → 最优。

1.6-12原创 · 沉没成本

Ming paid $40 for a nonrefundable concert ticket. On the night of the concert, a friend invites him to a free dinner that he values at $60. Ming values attending the concert at $50, and he cannot do both. A rational Ming will

go to the concert, because he has already paid $40
go to the concert, because $50 + $40 is greater than $60
go to the dinner, because the dinner is free
go to the dinner, because $60 is greater than $50
be indifferent, because the net benefits are equal

$40 是沉没成本，无论去哪里都拿不回来，不影响决策。只比较现在的选择：晚餐 $60 > 演唱会 $50 → 去晚餐（去晚餐的机会成本是演唱会的 $50）。(C) 理由错误：晚餐“免费”并不是选它的原因。

ΣSummary 单元总结与易错点

1.1 Scarcity

无限欲望 vs 有限资源 → 必须选择。机会成本 = 次优选择的价值（只算一个），常用“放弃了多少个另一种东西”表示。四要素：land（rent）、labor（wages）、capital（interest）、entrepreneurship（profit）。钱不是资本；已有知识是 non-rival，可能不稀缺。实证可检验，规范含价值判断。

1.2 Economic Systems

三个基本问题：what / how / for whom。市场经济：私有产权 + 价格机制 + 利润激励；计划经济：公有 + 中央计划；传统经济：习俗；现实中都是混合经济。

1.3 PPC

曲线上 = 有效率；曲线内 = 无效率（失业）；曲线外 = 达不到。斜率 = 机会成本；外凸 = 机会成本递增。资源或技术变化才移动曲线，失业只让点落到曲线内。

1.4 Comparative Advantage

绝对优势比数量，比较优势比机会成本。产出型对方放分子，投入型自己放分子。贸易条件在两国机会成本之间才互利；贸易让消费超出 PPC。

1.5 Cost-Benefit

理性 = 净收益（TB − TC）最大。收益：消费者看效用，企业看总收入。经济成本 = 显性 + 隐性。经济利润 = TR − 显性 − 隐性。“几选一”的决策不能拆分，只能比总量。

1.6 Marginal Analysis

MB > MC 多做，MB < MC 少做，MB = MC 最优。沉没成本、固定成本不影响最优数量。边际效用递减；MU = 0 时 TU 最大。预算线 P_XX + P_YY = I。效用最大化：MU_X/P_X = MU_Y/P_Y 且钱花完。

易错点 TOP 10

机会成本把所有放弃的选项加起来 ✗ → 只算次优的那一个。
“免费”的东西没有机会成本 ✗ → 时间和资源都有机会成本。
钱 / 股票是资本 ✗ → 是金融资本，不是生产要素。
失业让 PPC 内移 ✗ → 点移到曲线内，曲线不动。
某一种商品技术进步让 PPC 整体外移 ✗ → 只有该商品的截距外移。
绝对优势决定贸易方向 ✗ → 比较优势决定。
产出型和投入型用同一个公式 ✗ → 产出型对方放分子，投入型自己放分子。
只比较 MU 决定多买哪个 ✗ → 比较 MU / P。
把固定成本平摊到每一单位上再做决策 ✗ → 只比较这一单位的 MB 和 MC。
机会成本写成“得到了什么” ✗ → 是放弃了什么，并写上单位。

✎Unit 1 Test 单元测验

15 道选择题，全部选自历年 AP 真题（与各节练习不重复），建议用时 18 分钟（AP 考试约每题 70 秒）。先全部选完，再点底部“交卷”查看得分和解析。

T12023 AP Micro 国际卷 Q48

Scarcity leads to which of the following?

Unemployed resources
Absolute advantage
Opportunity cost
Efficiency
Monopolies

稀缺 → 必须选择 → 机会成本。

T22021 AP Micro 国际卷 Q44

Which of the following is NOT an example of physical capital?

A delivery truck
A warehouse
Office furniture
Machinery
Land

Land 是自然资源，不是人造的物质资本。

T32021 AP Micro 国际卷 Q21

In a command economy, the quantity of computers produced would be determined by

factory owners
the government
consumers and producers
international trade
the wealthy

计划经济中，生产多少台电脑由政府决定。

T42021 AP Micro 国际卷 Q24

Where on a graph of a production possibilities curve would a point showing that an economy is using its resources efficiently be located?

On the production possibilities curve
Inside the production possibilities curve
Beyond the production possibilities curve
On the y-axis and below the production possibilities curve
On the x-axis and below the production possibilities curve

曲线上的点 = 资源被充分且有效地利用。

T52000 AP Micro Q32

Good X	Good Y
1,000	0
990	100
980	200
970	300

The table below represents points on an economy's current production possibilities curve.

The opportunity cost of increasing the production of good Y from 0 to 200 is

1,000 units of X
980 units of X
200 units of X
20 units of X
5 units of X

Y 从 0 增加到 200，X 从 1,000 减少到 980，放弃 20 units of X。

T62013 AP Micro Q18

Assume that an economy produces televisions and shoes. Which of the following would cause the production possibilities curve for this economy to shift outward?

An increase in the labor force
An increase in the prices of both goods
An increase in the prices of resources used to produce both goods
A decrease in the demand for shoes
A change in consumers’ tastes in favor of televisions

劳动力增加 = 资源增加 → PPC 外移。价格、需求、偏好变化都不移动 PPC。

T72012 AP Micro Q2

Which of the following explains why a production possibilities curve is often represented as concave (bowed out) from the origin?

The law of demand
The law of supply
Constant returns to scale
Decreasing opportunity cost
Increasing opportunity cost

外凸 PPC = 机会成本递增（资源不能完美适用于两种生产）。

T82012 AP Micro Q16

Assume both Italy and Greece produce only two goods: wine and olive oil. If Italy holds a comparative advantage in the production of wine, then which of the following statements is NOT true?

Italy must hold an absolute advantage in the production of wine.
Greece holds a comparative advantage in the production of olive oil.
Italy’s opportunity cost of producing one additional unit of wine is lower than Greece’s.
Greece’s opportunity cost of producing one additional unit of olive oil is lower than Italy’s.
If trade is open between them, these countries have an incentive to trade.

比较优势不需要绝对优势，所以 (A) “必须有绝对优势”不成立（NOT true）。(B)(C)(D)(E) 都是比较优势的直接推论。

T92013 AP Micro Q31

	Brazil	Spain
Corn	2 hours of labor	4 hours of labor
Shoes	8 hours of labor	12 hours of labor

The table above shows the amount of labor required to produce a unit of corn and a unit of shoes in Brazil and Spain. If both countries have equal numbers of workers, what pattern of international trade between Brazil and Spain is most likely to emerge?

Brazil will export both corn and shoes.
Spain will export both corn and shoes.
No mutually beneficial trade can occur.
Brazil will export corn and import shoes.
Brazil will import corn and export shoes.

投入型。1 单位玉米的机会成本：Brazil = 2/8 = 0.25 双鞋，Spain = 4/12 ≈ 0.33 双 → Brazil 有玉米的比较优势，出口玉米、进口鞋。Brazil 两样都用时更少（有两项绝对优势），但贸易方向只看比较优势。

T102024 AP Micro Q17

	Portugal	Brazil
Chair	1 hour	2 hours
Desk	4 hours	3 hours

The table provided shows the number of labor hours required to produce one chair OR one desk in Portugal and Brazil. Which of the following is true if each country specializes in the production of the good in which it has a comparative advantage?

Neither country will be willing to trade.
Trade will be mutually beneficial if 1 desk is exchanged for 1 chair.
Trade will be mutually beneficial if 1 desk is exchanged for 5 chairs.
Portugal will specialize in producing chairs, and Brazil will specialize in producing desks.
Portugal will specialize in producing desks, and Brazil will specialize in producing chairs.

投入型。1 把椅子的机会成本：Portugal = 1/4 张书桌，Brazil = 2/3 张 → Portugal 专门做椅子，Brazil 专门做书桌。1 张书桌的机会成本：Portugal 4 把椅子，Brazil 1.5 把，互利的条件是 1 desk 换 1.5–4 把椅子，所以 (B) 1 把、(C) 5 把都不行。

T112024 AP Micro Q1

Economists assume that rational individuals make choices by comparing the marginal benefit of an activity to its

marginal utility
marginal revenue
marginal cost
average total cost
average revenue

理性决策：比较边际收益与边际成本。

T122019 AP Micro 练习卷 Q28

Levels of cleanup	Total cost of cleanup ($)	Total benefit of cleanup ($)
0	0	0
1	7	45
2	37	80
3	92	105
4	172	125
5	272	140

The table above shows the total cost and the total benefit of cleaning up pollution in a community. Which of the following cleanup levels is socially optimal?

净收益 = TB − TC：38, 43, 13, −47, −132，第 2 级最大。边际法：第 2 级 MB 35 > MC 30，第 3 级 MB 25 < MC 55。

T132017 AP Micro 练习卷 Q23

An art student spends all of her income on pencils and drawing pads. The student currently buys 30 pencils at $1 each and 10 pads at $5 each. If the marginal utility of the 30th pencil is 100 utils and the marginal utility of the 10th pad is 400 utils, to maximize utility the student should change her purchases of pencils and pads in which of the following ways?

Pencils: Not change；Pads: Buy more
Pencils: Buy more；Pads: Buy more
Pencils: Buy more；Pads: Buy less
Pencils: Buy less；Pads: Buy more
Pencils: Buy less；Pads: Buy less

MU/P：铅笔 = 100/1 = 100，画本 = 400/5 = 80。铅笔每元效用更高 → 多买铅笔、少买画本。

T142022 AP Micro 国际卷 Q30

When marginal utility from consuming a good is zero, the total utility from consuming the good is

zero
negative
maximized
rising at a constant rate
equal to marginal utility per dollar spent on the good

MU = 0 时，再多消费一单位不再增加总效用，总效用达到最大。

T152021 AP Micro 国际卷 Q60

Josephine is buying candy and gum. If she is maximizing her utility for the combination of candy and gum she buys, which of the following must hold?

Marginal utility of candy ÷ price of candy = marginal utility of gum ÷ price of gum
Total utility of candy ÷ price of candy = total utility of gum ÷ price of gum
Marginal utility of candy ÷ total utility of candy = marginal utility of gum ÷ total utility of gum
Marginal utility of candy × price of candy = marginal utility of gum × price of gum
Total utility of candy × price of candy = total utility of gum × price of gum

效用最大化法则：MU_candy/P_candy = MU_gum/P_gum。

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FRQFree-Response Practice 自由问答

下面三道是 AP 真题大题中考 Unit 1 的部分，评分标准依照 College Board 官方 Scoring Guidelines 整理；最后一道是综合练习原创题。先在纸上完整写出答案（包括画图），再展开评分标准对照。

FRQ 1 · 2018 AP Micro FRQ Q3 · 5 分 · 机会成本与边际分析真题

Nirali is a student at the University of Ainsley. She has 5 hours to study for two exams today. The tables below show Nirali's expected scores given the amount of time she studies for each exam.

Hours studying Microeconomics	Expected score (Micro)
5	100
4	96
3	90
2	82
1	60
0	0

Hours studying History	Expected score (History)
0	0
1	40
2	60
3	72
4	77
5	80

(a) Nirali spends 3 hours studying microeconomics and 2 hours studying history. Calculate her gain from the second hour spent studying history.
(b) Calculate Nirali's opportunity cost of the second hour spent studying history.
(c) Assume Nirali increases the time she allocates to studying history. What happens to the opportunity cost of studying history? Explain.
(d) Assume that Nirali has a goal of maximizing the sum of her test scores. How many hours should she study for each exam?
(e) Nirali learns that her tennis practice has been canceled, freeing up an additional hour for studying. Given your answer to part (d), will Nirali allocate the additional hour to studying microeconomics or to studying history to maximize the sum of her test scores? Explain using marginal analysis.

Point	得分要求与解析
(a) 1 pt	History 从 1 小时到 2 小时：60 − 40 = 20 points。
(b) 1 pt	第 2 小时用来学历史，就要从经济里拿走 1 小时（4 → 3 小时）：96 − 90 = 6 points（官方也接受 6/20）。注意表格的排列方向：经济表是从 5 小时往下排的。
(c) 1 pt	Increases。每多花 1 小时学历史，经济要放弃的分数越来越多（第 1 小时放弃 4 分、第 2 小时 6 分、第 3 小时 8 分……），即机会成本（边际成本）递增。
(d) 1 pt	2 hours Micro + 3 hours History。逐一比较总分：(5,0)=100，(4,1)=136，(3,2)=150，(2,3)=82+72=154，(1,4)=137，(0,5)=80。
(e) 1 pt	Microeconomics。多 1 小时学经济（2 → 3 小时）总分 +8（90 − 82），多 1 小时学历史（3 → 4 小时）只 +5（77 − 72），8 > 5。必须写出两边的边际增加量进行比较才得分。

联系：这道题和例题 5“期末周的 PPC”是同一个模型——两门课的分数构成一条外凸的 PPC。

FRQ 2 · 2023 AP Micro FRQ Set 1 Q2 (a)–(c) · 3 分 · 比较优势真题

The graph shows the production possibilities curves for Northland and Southland.

按原题重绘：两国纵轴截距都是 100 bushels；横轴截距 Southland 50 yards、Northland 300 yards

(a) Which country has a comparative advantage in producing wheat? Explain using numbers.
(b) Identify a specific number of yards of cloth that could be traded for 10 bushels of wheat and would be mutually beneficial to Northland and Southland.
(c) Southland's maximum possible output of wheat falls from 100 bushels to 75 bushels. Assuming no other changes, will Southland have a comparative advantage in producing cloth? Explain using numbers.

原题 (d) 考负外部性与定额税，属于 Unit 3/6，此处略去。

Point	得分要求与解析
(a) 1 pt	Southland。Southland 生产 1 bushel 小麦的机会成本 = 50/100 = 1/2 yard of cloth，低于 Northland 的 300/100 = 3 yards。
(b) 1 pt	10 bushels 小麦的机会成本：Southland 5 yards，Northland 30 yards。答 5 到 30 之间的任一具体数字（如 15 yards）。注意题目问的是“10 bushels”，不是 1 bushel。
(c) 1 pt	No。变化后 Southland 生产 1 yard 布的机会成本 = 75/50 = 1.5 bushels，仍高于 Northland 的 100/300 = 1/3 bushel，比较优势仍在 Northland。

FRQ 3 · 2025 AP Micro 国际卷 FRQ Q2 Part A–B · 3 分 · 效用最大化真题

Yuni is a utility-maximizing consumer. The table shows the marginal utility for Yuni when she consumes tennis rackets and shirts.

Quantity of tennis rackets	MU of tennis rackets (utils)	Quantity of shirts	MU of shirts (utils)
1	600	1	400
2	400	2	300
3	200	3	200
4	100	4	100
5	50	5	50
6	0	6	25

Part A: If Yuni is allowed to choose either one tennis racket or two shirts for free, which of these two options will Yuni choose? Explain using numbers.
Part B: Suppose instead the price of a tennis racket is $100, the price of a shirt is $50, and Yuni's income is $500. Yuni spends all her income on tennis rackets and shirts.
(i) If Yuni purchases 2 tennis rackets, what is the maximum quantity of shirts Yuni can purchase?
(ii) What is the combination of tennis rackets and shirts that maximizes Yuni's total utility? Explain your answer using marginal analysis and numbers.

原题 Part C 考正外部性与补贴，属于 Unit 6，此处略去。

Point	得分要求与解析
A 1 pt	Two shirts。两件衬衫的总效用 = 400 + 300 = 700 utils > 一支球拍的 600 utils。免费时不用除以价格，直接比较总效用。
B(i) 1 pt	2 支球拍花 $200，剩 $300，最多买 300 ÷ 50 = 6 shirts。
B(ii) 1 pt	3 tennis rackets and 4 shirts。最后一支球拍 MU/P = 200/100 = 2 utils/$，最后一件衬衫 MU/P = 100/50 = 2 utils/$，两者相等，且正好花完 $500（= 3×$100 + 4×$50）。

做法：先把每一行的 MU/P 算出来——球拍 6, 4, 2, 1, 0.5, 0；衬衫 8, 6, 4, 2, 1, 0.5——再从最高的开始买，直到钱花完。

FRQ 4 · 综合练习（约 7 分） · 原创

Countries Alpha and Beta each use all of their resources to produce only rice and cloth, and both have constant opportunity costs. In one month, Alpha can produce either 600 tons of rice or 200 bolts of cloth. Beta can produce either 400 tons of rice or 200 bolts of cloth.

(a) Draw a correctly labeled production possibilities curve for Alpha with cloth on the horizontal axis. Label the numerical values of the intercepts.
(b) Which country has the absolute advantage in producing rice? Explain.
(c) Calculate Beta's opportunity cost of producing one bolt of cloth.
(d) Which country has the comparative advantage in producing cloth? Explain using opportunity costs.
(e) Suppose the two countries specialize and trade at 1 bolt of cloth for 2.5 tons of rice. Will both countries benefit? Explain.
(f) Suppose Alpha experiences a technological improvement in cloth production only. On your graph in part (a), show the effect on Alpha's PPC.
(g) After the change in part (f), will Alpha's opportunity cost of producing one ton of rice increase, decrease, or stay the same?

Point	Scoring standard 得分要求
(a) 1 pt	一条直线 PPC，纵轴 Rice、横轴 Cloth，截距标为 600（rice）和 200（cloth）。轴标签缺失或截距画反不得分。
(b) 1 pt	Alpha，因为用同样的资源 Alpha 能生产更多大米（600 > 400）。只写国家名、不写理由不得分。
(c) 1 pt	400 / 200 = 2 tons of rice。
(d) 1 pt	Beta。Beta 生产 1 匹布的机会成本是 2 吨大米，低于 Alpha 的 600/200 = 3 吨大米。必须写出两国的机会成本进行比较。
(e) 1 pt	Yes。2.5 吨大米在两国机会成本（2 和 3）之间：Beta 每出口 1 匹布换回 2.5 吨大米，多于自己的机会成本 2 吨；Alpha 每进口 1 匹布只付 2.5 吨大米，少于自己生产的机会成本 3 吨。
(f) 1 pt	横轴（cloth）截距向右移动，纵轴（rice）截距仍为 600 不变。
(g) 1 pt	Increase。1 吨大米的机会成本 = 能生产的布 / 能生产的大米 = cloth 截距 / 600；布的截距变大而大米截距不变，所以生产大米要放弃的布更多。

FRQ 答题提醒

Explain 一定要给出理由，比较优势题必须写出两边的机会成本数字。
画图：两条轴都要标商品名，截距标数字，移动后的新曲线要和原曲线区分开（标 PPC₁、PPC₂ 或用箭头）。
机会成本要写单位：“2 tons of rice”，不要只写“2”。

JL · AP Microeconomics · Unit 1 Basic Economic Concepts · 题目标签：真题历年 AP 考试原题（含 College Board 练习卷、国际卷），答案均对照官方答案键并重新验算 · 原创依照 AP 题型原创