十月份冲刺来临之际，小编整理出2015年至今的历年demand、supply 以及各类elasticity的data response。
我们可以发现D-S model每次必考，分值在10分左右，占总分值12.5%。
这次小编将送给同学们一篇2019年January的data例文，最后讲解2019年六月份新考纲第12题。
2019-1-10
Sample：
（a）In Figure1, The lowest copper price in 2014 was $2.5 per pound. In August 2017, the copper price rose to $3.11 per pound, which was equivalent to a 7% increase from September 2014.
As mentioned in Extract 1, due to the continuous growth of Chinese economy, China's demand for metal keeps increasing, and China is the world's largest copper consumer, able to purchase 46% of the global copper output.In addition, because China's restrictions on recycled copper imports, mean that China will consume more newly - mined copper, so there will be more demand for copper in China.
As shown in the following diagram,Since China's demand for copper increased, the demand curve moved to the right from D1 to D2.P1,Q1 are the original equilibrium price and quantity, P2 and Q2 are the new equilibrium price and quantity, so in the copper market ,the price of copper has increased.
（b）price elasticity of demand refers the responsiveness of quantity demanded to a change in price ,and is calculated by dividing the percentage change in quantity demanded by the percentage change in price.if the value is between-1 and 0,this means the response of Qd is less than the change in price and the good is insensitive to a price change,it is price inelastic.
In the extract 2, there are no approximate substitutes in copper, that is to say, substitutes of copper have low availability.Although aluminum is sometimes used instead of copper in some industries, switching between the two metals involves costs and delays,this means that the demand of copper has not fallen much in a rush as prices go up.
(c) Price elasticity of supply refers the responsiveness of quantity supplied to a change in price ,and is calculated by dividing the percentage change in quantity supplied by the percentage change in price.if the value is less than 1,this means the response of Qs is less than the change in price and the good is insensitive to a price change,it is price inelastic.[knowledge]
According to the second paragraph in extract 2, firstly, due to the high fixed cost of developing new copper mines, such as large equipment, and the long start-up time, cooper's price increase will not lead to a large increase in supply in the short term.In addition, existing copper mining operations are approaching their current capacity, meaning existing copper mines cannot increase production.Finally, in this excerpt, it is noted that supply responds adequately only when prices rise substantially.In other words, the change in quantity supplied is less than the change in price.In summary, the supply of copper is inelastic.If the supply is inelastic, the graph is shown below:[application analysis]
In the short term, Cooper's supply may be inelastic, but in the long term, as prices rise, companies are more confident in investing in copper mines with better prospects, and as production increases, the average cost of copper mines will decrease, so copper supply will increase.
In the context of the global economic slowdown, many enterprises also began to store newly mined copper. As the storage increased, the market could increase the supply when the market price increased, instead of relying on production to provide Cooper.[evaluation]
2019-June-12
解析：这是2019年六月份edxecel新版考纲真题的第12题data response，我们在开始审题时发现这是一篇关于meat market的extract，讨论对象lamb，figure1首先显示lamb的income elasticity，我们需要注意一下，YED of lamb为-0.146，这就意味着lamb此时对于consumers来说是inferior good；然后继续审题，figure 2 显示16年march至18年march内lamb的world price变化，直观的感受就是价格波动上升。此时，同学们应该能够猜得出来本次考试D-S考定了！同学们可以在表格旁边做个标记。
继续阅读材料发现，Extract A的标题即为“the price of lamb”所以我们便顺利找到影响lamb price 上升的reasons啦!
下面我们看下题目从而确定具体的答题思路：
Australia的real income上升2.7%，对lamb的quantity demanded会产生什么影响呢，我们迅速回想到Australia对lamb的YED是-0.146，所以我们根据YED=the percentage change of quantity demanded/the percentage change in income,所以可以得出the percentage change of quantity demanded为-0.39；以上分析到此结束，答题过程务必拿到4分。解释YED→figure1 →inferior good→condition→the percentage change of quantity demanded。
我们在第一次阅读材料后，已经几乎可以准确找到影响D-S的因素，所以此时我们着重整理解题思路。
如sample所示，我们在Application这一部分需要描述figure2显示the price change，然后在ExtractA中使用rising global incomes以及successful advertising两个条件作为导致demand for lamb的原因，在此引用条件也是application，不过请注意不允许照搬原句，这是考试局在examiner report中反复提到的问题。
之后同学们只需要分析条件导致demand 增加（有同学可能会怀疑在figure 1 中lamb是inferior，而income 上升所以the demand for lamb应该下降，那老师就要说你想多了，因为figure1 是Australia 境况，这边说的是global context），一定要画图！
