📚 Year 12 WJEC Economics Mock Unit Test Analysis | 12年级WJEC经济单元模拟卷解析
Mock exams are a cornerstone of effective revision for WJEC Year 12 Economics. They not only test your knowledge of key microeconomic concepts such as opportunity cost, elasticity and market failure, but also train you to apply command words like ‘analyse’ and ‘evaluate’ under timed conditions. In this article, we deconstruct a typical unit test paper, question by question, explaining the correct answers, common pitfalls and the deeper economic reasoning behind each response. Whether you are preparing for a classroom assessment or simply reinforcing your understanding of the WJEC specification, this walkthrough will sharpen your exam technique.
模拟考试是WJEC 12年级经济学科高效复习的基石。它不仅考察你对机会成本、弹性和市场失灵等核心微观经济概念的掌握，还训练你在限时条件下运用“分析”、“评估”等指令词作答的能力。本文将对一套典型的单元测试卷进行逐题拆解，解释正确答案、常见误区以及每个答案背后的深层经济学逻辑。无论你是在准备课堂测验，还是单纯想巩固对WJEC考纲的理解，这次解析都将提升你的应试技巧。
1. Opportunity Cost and Production Possibility Frontier | 第1题：机会成本与生产可能性边界
The question presented a table showing the combinations of consumer goods and capital goods an economy can produce with all its resources. Students were asked to calculate the opportunity cost of moving from combination B to C, where consumer goods rose from 50 to 70 units while capital goods fell from 40 to 25 units.
题目给出一个表格，展示某经济体利用全部资源所能生产的消费品与资本品组合。要求学生计算从组合B移动到组合C时的机会成本，其中消费品从50单位增加到70单位，而资本品从40单位下降到25单位。
Opportunity cost is defined as the value of the next best alternative forgone. Here, the economy sacrifices 15 units of capital goods (40 − 25) to gain 20 units of consumer goods. Therefore, the opportunity cost of producing one additional unit of consumer goods is 15/20 = 0.75 capital goods. A common mistake was to invert the ratio, giving 1.33, which would be the opportunity cost of capital goods instead. The PPF diagram that accompanied the question also tested the law of increasing opportunity cost, as the boundary bowed outwards.
机会成本被定义为所放弃的次优选择的价值。在这里，经济体为了多获得20单位消费品，牺牲了15单位资本品（40 − 25）。因此，每多生产一单位消费品的机会成本为15/20 = 0.75单位资本品。常见错误是把这个比率颠倒过来，得出1.33，这其实变成了资本品的机会成本。随题目给出的生产可能性边界（PPF）图向外凸出，也考查了机会成本递增规律。
To score full marks, you needed to state clearly: ‘The opportunity cost of moving from B to C is 15 capital goods, or 0.75 capital goods per extra consumer good’. Linking this to the diagram by noting the increasing gradient of the PPF showed deeper understanding.
要拿到满分，你需要清晰陈述：“从B移动到C的机会成本是15单位资本品，或者说每多获得一单位消费品的机会成本是0.75单位资本品”。如果能结合图形指出PPF的斜率递增，则能展示更深层次的理解。
2. Price Elasticity of Demand Calculation | 第2题：需求价格弹性计算
This question supplied data: when the price of a cinema ticket rose from £8 to £10, the quantity demanded fell from 600 tickets per week to 450. Students were required to calculate the price elasticity of demand (PED) using the standard formula and interpret the coefficient.
本题提供了一组数据：电影票价格从8英镑上涨至10英镑，每周的需求量从600张下降到450张。要求用标准公式计算需求价格弹性（PED）并解释该系数的含义。
The formula for PED is %ΔQd ÷ %ΔP. The percentage change in quantity demanded is: (450 − 600) ÷ 600 × 100 = −25%. The percentage change in price is: (10 − 8) ÷ 8 × 100 = 25%. Thus, PED = −25% ÷ 25% = −1.0. The negative sign is conventionally ignored because we are interested in magnitude, so the elasticity is unitary elastic (PED = 1).
PED的计算公式是%ΔQd ÷ %ΔP。需求量的变动百分比为：(450 − 600) ÷ 600 × 100 = −25%。价格的变动百分比为：(10 − 8) ÷ 8 × 100 = 25%。因此，PED = −25% ÷ 25% = −1.0。按照惯例，负号常被忽略，因为我们只关心绝对值大小，所以该弹性为单位弹性（PED = 1）。
Interpretation matters: when demand is unit elastic, a given percentage change in price leads to an equal percentage change in quantity demanded, leaving total revenue unchanged. In this scenario, total revenue at £8 was £4,800; at £10, it was £4,500? Wait, check: 600 × £8 = £4,800; 450 × £10 = £4,500. That suggests revenue fell, so it’s not perfectly unit elastic – the calculation needs precise midpoint method for arc elasticity in some boards, but WJEC often accepts the simple percentage method for small changes. The discrepancy arises because the base is initial value. However, the coefficient of -1.0 indicates unitary elasticity at that arc, and revenue should remain roughly constant. In exam conditions, you would note that the slight revenue fall reflects the use of the simple point formula; the key is to show your working. A common pitfall is forgetting to multiply by 100 or mixing up the base values.
解释也至关重要：需求为单位弹性时，价格变动某一百分比会导致需求量同比例变动，总收益保持不变。在此场景中，价格为8英镑时总收益为4,800英镑；10英镑时，450 × 10 = 4,500英镑，收益下降了一点，这说明简单点弹性公式的局限。在考试中，你只需展示计算步骤，指出系数为-1表明单位弹性，并可以简要提一句因采用初始值计算导致微小偏差。常见失误是忘记乘以100，或者把基数搞混。
3. Market Equilibrium and Shifts in Demand | 第3题：市场均衡与需求移动
A diagram showed the market for oat milk. The initial equilibrium was at price P1 and quantity Q1. A new health report claimed that oat milk reduces cholesterol significantly. Students had to show the new equilibrium and explain how consumer behaviour drives the shift.
题目给出了一幅燕麦奶市场的图形。初始均衡在价格P1和数量Q1处。一份新的健康报告声称燕麦奶能显著降低胆固醇。学生需要标出新的均衡，并解释消费者行为如何驱动曲线的移动。
The health report acts as a positive change in tastes and preferences, which is a non-price determinant of demand. Consequently, the demand curve shifts to the right (from D1 to D2). At the original price P1, there is now excess demand (a shortage), putting upward pressure on price. The price rises until a new equilibrium is reached at a higher price P2 and higher quantity Q2. The supply curve does not shift initially because the change is on the demand side.
健康报告相当于消费者口味与偏好的积极变化，这是需求的非价格决定因素。因此，需求曲线向右平移（从D1到D2）。在原价格P1处，市场出现超额需求（短缺），推动价格上升。价格持续上涨，直到在更高的价格P2和更高的数量Q2处达到新均衡。供给曲线最初不会移动，因为变化发生在需求侧。
In your answer, you must refer to the diagram explicitly: ‘The rightward shift of the demand curve from D1 to D2 leads to…’ and ‘Producers respond to the higher price by expanding quantity supplied along the existing supply curve.’ Avoid saying ‘supply increases’ when you mean ‘quantity supplied increases’. This distinction is crucial for WJEC marking.
作答时，你必须明确引用图形：“需求曲线从D1到D2的右移导致……”以及“生产者为应对更高的价格，沿着原有的供给曲线扩大供应量”。避免在表达“供应量增加”时误说成“供给增加”。这个区分对于WJEC的评分至关重要。
4. Incidence of an Indirect Tax | 第4题：间接税的归宿
A multiple-choice question asked: ‘The government imposes a £2 per unit tax on a good with highly elastic demand and inelastic supply. Who bears the greater burden of the tax?’ The options were: A) Consumers, B) Producers, C) Both equally, D) The government. The correct answer is B, producers.
一道选择题问道：“政府对某种需求高度弹性而供给缺乏弹性的商品征收每单位2英镑的税。谁将承担更大的税负？”选项为：A) 消费者，B) 生产者，C) 双方均等，D) 政府。正确答案是B，生产者。
Tax incidence depends on relative price elasticity. When demand is highly elastic, consumers are very responsive to price changes; they will simply stop buying if the price rises. Thus, producers cannot pass much of the tax burden onto consumers in the form of higher prices. Instead, producers must absorb most of the tax, resulting in a lower price received net of tax. The supply inelasticity also means producers are less able to adjust quantity supplied in response to a price drop, further increasing their burden. A common error was choosing C, misapplying the idea that the burden splits equally, which only occurs when elasticities are equal.
税负归宿取决于相对价格弹性。当需求高度弹性时，消费者对价格变化非常敏感；价格一旦上涨，他们便停止购买。因此，生产者无法以提价形式将大部分税负转嫁给消费者。相反，生产者必须自行吸收大部分税收，导致他们税后实得价格下降。供给缺乏弹性也意味着生产者难以根据价格下跌调整供应量，进一步加重了他们的负担。常见错误是选择C，误以为税负总是均等分担，这仅发生在双方弹性相等时。
To reinforce this, we drew the diagram and showed the producer burden area (tax wedge between original supply and demand price) larger than the consumer burden area. Always label the new consumer price Pc and the new producer price Pp.
为了强化理解，我们画图并展示生产者负担区域（原供给价格与需求价格之间的税收楔子）大于消费者负担区域。记得总是标出新消费者价格Pc和新生产者价格Pp。
5. Positive Externalities and Under-Consumption | 第5题：正外部性与消费不足
The stimulus material described a local beekeeper whose bees pollinate neighbouring apple orchards, increasing fruit yields. Students were asked to explain why this leads to a market failure and to draw a diagram showing the welfare gain from government intervention.
题目材料描述了一位本地养蜂人，他的蜜蜂为相邻的苹果园授粉，提高了水果产量。要求学生解释这为何会导致市场失灵，并画出显示政府干预带来福利增益的图形。
Beekeeping generates a positive externality in consumption (or production, depending on perspective) because the orchard owners receive a free pollination service without paying for it. The private benefit to beekeepers is the revenue from honey; the external benefit is the additional apple yield. The social benefit (MSB) exceeds the private benefit (MPB). In a free market, beekeepers only consider their private benefit, so the equilibrium quantity Qm is less than the socially optimal quantity Qopt. This results in under-provision of beekeeping and a deadweight welfare loss (triangle between MSB and MPC at Qm).
养蜂活动产生了消费（或生产，视角度而定）的正外部性，因为果园主免费获得了授粉服务。养蜂人的私人收益来自蜂蜜销售；外部收益则是额外的苹果产量。社会收益（MSB）大于私人收益（MPB）。在自由市场中，养蜂人仅考虑私人收益，因此均衡数量Qm低于社会最优数量Qopt。这导致养蜂业的提供不足和一笔无谓福利损失（位于Qm处MSB和MPC之间的三角区）。
Government intervention, such as a subsidy equal to the external benefit, can shift the supply curve (or raise the MPB) to encourage output at Qopt. In the diagram, the welfare gain is the area of the deadweight loss that is eliminated. Students who confused positive externalities with negative ones drew the wrong triangles and lost marks.
政府干预，比如给予等于外部收益的补贴，可以使供给曲线移动（或提升MPB），从而激励产量达到Qopt。在图形中，福利增益即为被消除的无谓损失区域。那些将正外部性与负外部性混淆的学生画错了三角区域，因而失分。
6. Costs and Revenues in Perfect Competition | 第6题：完全竞争中的成本与收益
Here, a firm’s data showed output levels, total cost (£) and market price (constant at £12 per unit). Students had to identify the profit-maximising level of output and justify it using marginal analysis.
本题给出了一家企业的数据：产量水平、总成本（英镑）以及恒定的市场价格（每单位12英镑）。学生需要找出利润最大化产量，并使用边际分析说明理由。
Since the firm is a price-taker in perfect competition, marginal revenue (MR) equals price (£12). The profit-maximising rule is to produce where MR = MC, provided MC is rising. We calculated marginal cost (MC) as the change in total cost divided by the change in output. At output level 4, MC was £10; at output level 5, MC rose to £14. Thus, producing the 5th unit adds £14 to cost while only adding £12 to revenue, so profit falls. The optimal output is therefore 4 units, where MC (£10) is just below MR and the next unit would push MC above MR. Many students stopped at the rule ‘MR=MC’ but failed to check whether MC was crossing from below; at output 4, MC < MR and at output 5, MC > MR, confirming maximum total profit.
由于该企业是完全竞争中的价格接受者，边际收益（MR）等于价格（12英镑）。利润最大化规则是在MC上升的前提下，令产量达到MR = MC处。我们计算边际成本（MC）为总成本变动量除以产量变动量。在产量为4个单位时，MC为10英镑；产量为5个单位时，MC升至14英镑。因此，生产第5个单位将增加14英镑成本，却只增加12英镑收益，利润会下降。所以最优产量是4个单位，此时MC（10英镑）刚好低于MR，再增加一单位MC就会超过MR。许多学生只答了“MR=MC”规则，却未检验MC是否从下方穿越MR；在产量为4时，MC < MR，产量为5时，MC > MR，这确认了总利润最大化的位置。
7. Interpreting a Price Ceiling Diagram | 第7题：价格上限图形解读
The paper included a graph of a maximum price (price ceiling) set below the free-market equilibrium for rented housing. Students were asked to describe the likely outcome and evaluate the policy’s effects.
试卷中有一幅图，显示租金住房市场设定了低于自由市场均衡的最高限价（价格上限）。学生需要描述可能的结果，并评估该政策的效果。
A maximum price set below equilibrium creates a persistent shortage because quantity demanded (Qd) exceeds quantity supplied (Qs) at that price. In the housing market, this leads to a shortage of rental properties, long waiting lists and potentially a black market where tenants pay extra ‘key money’ to secure a lease. The policy’s intention is to make housing affordable for low-income families, but the unintended consequences include reduced incentive for landlords to maintain properties or supply new ones, leading to a deterioration in housing quality. An evaluative comment might note that the shortage could be mitigated by government provision of social housing, which would shift the supply curve rightwards, or by a parallel subsidy to encourage building.
设定在均衡价格之下的最高限价会导致持续性短缺，因为在该价格水平上需求量（Qd）超过供给量（Qs）。在住房市场中，这会引发租赁房屋短缺、漫长的等候名单，甚至可能出现黑市，租户为获得租约额外支付“钥匙费”。该政策的初衷是让低收入家庭住得起房，但意外后果包括房东维护房产或提供新房源的激励下降，导致住房质量恶化。评价性见解可以指出，政府提供社会住房可使供给曲线右移，或通过并行补贴鼓励建房，从而缓解短缺。
In your answer, always relate the analysis to the context given, e.g. ‘for a city like Cardiff where student population surges each autumn’. WJEC rewards applied analysis.
作答时，始终把分析与所给情境联系起来，例如“对于像卡迪夫这样每年秋季学生人口激增的城市”。WJEC看重应用性分析。
8. Essay Question: Analyse the Impact of a Sugar Tax | 第8题：论述题：分析糖税的影响
A 12-mark essay asked: ‘Analyse the likely microeconomic effects of a tax on sugary drinks.’ The mark scheme demanded a diagram with a leftward shift of the supply curve, identification of tax incidence on consumers and producers, and a discussion of external costs associated with sugar consumption.
一道12分的论述题要求：“分析对含糖饮料征税可能产生的微观经济影响。”评分标准要求画出供给曲线左移的图形，识别出消费者和生产者的税负，并讨论与糖消费相关的外部成本。
Key analysis points: The tax shifts the supply curve upwards by the amount of the tax (S1 to S2), raising the price from P to Pc and reducing quantity from Q to Qt. Because the demand for sugary drinks tends to be price inelastic among habitual consumers, a greater share of the tax falls on consumers. The external costs – such as increased NHS spending on obesity-related diseases – are negative externalities in consumption, meaning the free-market equilibrium over-consumes sugar relative to the social optimum. The tax internalises some of this externality, reducing consumption and generating government revenue that could ring-fence for health programmes. However, it is regressive, hitting lower-income households proportionally harder. Students who included an evaluative paragraph considering alternative policies like minimum pricing or banning advertising scored top marks.
关键分析点：税收使供给曲线上移相当于税额的幅度（从S1到S2），价格从P升至Pc，数量从Q降至Qt。由于习惯性消费者对含糖饮料的需求往往缺乏价格弹性，较大份额的税负落在消费者身上。外部成本——如因肥胖相关疾病增加的NHS支出——属于消费的负外部性，这意味着自由市场均衡下的糖消费量超出了社会最优水平。征税使这部分外部性内部化，既减少了消费，又为政府创造了可用于健康项目的专项收入。然而，这种税是累退的，给低收入家庭带来更沉重的相对负担。在评价段落中，如果能考虑最低定价或禁止广告等替代政策的学生，能拿到高分。
9. Labour Market Forces: National Living Wage Evaluation | 第9题：劳动力市场分析：国家生活工资评估
This data-response question provided a table showing the UK’s National Living Wage (NLW) rate rising to £11.44 per hour for workers aged 21+, and statistics on low-pay sectors. Students had to apply demand and supply analysis to labour markets.
这道数据回应题提供了一个表格，显示英国国家生活工资（NLW）上调至21岁及以上工人每小时11.44英镑，以及低薪行业的统计数据。学生需要运用劳动力市场的供求分析。
The NLW is a price floor in the labour market. If set above the equilibrium wage for low-skilled work, it creates a surplus of labour – classical unemployment. The diagram shows the wage rate above equilibrium, causing quantity of labour supplied to exceed quantity demanded. However, the magnitude of unemployment depends on the elasticity of demand for labour. In sectors like care, where demand is relatively inelastic because substitution by capital is difficult, the employment effect may be small. Moreover, efficiency wage theory suggests higher wages could boost productivity and reduce staff turnover, potentially offsetting job losses. Students who simply stated ‘it causes unemployment’ without considering these nuances missed evaluation marks. The correct answer integrated data from the table, noting that the adult social care sector, where a high proportion of workers were previously paid just below the new NLW, might see only minor disemployment effects but significant wage bill increases for employers.
国家生活工资是劳动力市场中的价格下限。如果设定在低技能工作的均衡工资之上，便会产生劳动力过剩——即古典失业。图形显示工资率高于均衡水平，导致劳动力供给量超过需求量。然而，失业的实际幅度取决于劳动力需求的弹性。在护理等需求相对缺乏弹性的行业，因为资本替代人工的难度较大，就业效应可能很小。此外，效率工资理论表明，较高的工资可以提高生产率、降低员工流失率，从而可能在某种程度上抵消岗位减少。那些只简单回答“会导致失业”而未考虑这些细微差别的学生会丢失评价分数。正确答案应整合表格数据，指出在成人社会护理行业，许多工人此前的薪酬刚好略低于新标准，因此可能只会出现轻微的失业效应，但雇主的工资总支出会显著增加。
10. Overall Exam Technique for WJEC Economics Unit Tests | 第10题：WJEC经济单元测试通用应试技巧
Based on this mock paper, several strategies emerge. First, always define key terms in the opening sentence of an ‘explain’ or ‘analyse’ question – for instance, ‘PED measures the responsiveness of quantity demanded to a change in price’. Second, integrate diagrams seamlessly: refer to specific labels (e.g. ‘the shaded triangle represents deadweight loss’) and avoid drawing a diagram without explaining it in the text. Third, match the length of your answer to the mark allocation; a 4-mark question typically requires two developed points with application. Fourth, for evaluation, use phrases like ‘it depends on the price elasticity’, ‘in the short run versus the long run’, or ‘assuming ceteris paribus, but in reality…’. Finally, practise the arithmetic of elasticity calculations until you can complete them quickly and accurately, as these are guaranteed marks if shown step-by-step.
从这套模拟卷中，可以总结出几条策略。第一，在“解释”或“分析”类题目的开头句，总要定义关键术语——例如，“PED衡量需求量对价格变动的反应程度”。第二，无缝整合图形：明确引用图中的具体标注（如“阴影三角形代表无谓损失”），避免画出图形却不加文字解释。第三，答题篇幅要与分值匹配；一道4分的题目通常需要展开两个观点并结合情境。第四，评估时可使用诸如“取决于价格弹性”、“短期与长期对比”，或“假设其他条件不变，但现实中……”等用语。最后，反复练习弹性计算的算术过程，直到你能迅速且准确地完成，这些步骤只要分步展示就是稳拿的分数。
Keep a revision note of your common mistakes – like forgetting the negative sign in PED or confusing movements along the curve with shifts – and review them before the test. The WJEC paper rewards precision, so accuracy in defining and applying economic theory is paramount.
把你常犯的错误整理成复习笔记——比如忘记PED的负号，或者混淆沿曲线移动与曲线平移——并在考前回顾。WJEC试卷看重精确性，因此准确界定并运用经济理论至关重要。
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