GWD3-4没有人问过吗？？？好疑惑阿！！！

Q4:

In the year following an eight-cent increase in the federal tax on a pack of cigarettes, sales of cigarettes fell ten percent.  In contrast, in the year prior to the tax increase, sales had fallen one percent.  The volume of cigarette sales is therefore strongly related to the after-tax price of a pack of cigarettes.

The argument above requires which of following assumptions?

1. During the year following the tax increase, the pretax price of a pack of cigarettes did not increase by as much as it had during the year prior to the tax increase.
2. The one percent fall in cigarette sales in the year prior to tax increase was due to a smaller tax increase.
3. The pretax price of a pack of cigarettes gradually decreased throughout the year before and the year after the tax increase.
4. For the year following the tax increase, the pretax price of a pack of cigarettes was not eight or more cents lower than it had been the previous year.
5. As the after-tax price of a pack of cigarettes rises, the pretax price also rises.

我选E，因为只有税前的价格上去了，销售量才能降下来啊，

但为什么选D呢

没有人回答，阿。真痛苦哦！！

条件1。+8cents税以后，sales 下降 10%

条件2。在+8cents的前一年， sales 下降1%

结论： 销售量和税后价格紧密相关；

D:确保了+8cents以后价格要比前一年还要高，从而说明涨价了以后销售明显下降（即使只有1cents）完美地结合了条件1和2，顺利搭桥到达结论；

E:税后价格上升，税前价格也上升，无关地有点莫名其妙，当然排除。。

如果是E的話～不就代表pretax price才是造成銷售下滑的原因嗎？這樣就counter

原來的argument了

原來是說after tax與sales有高度關連性，所以要排除pre-tax下降的可能。

這就跟作實驗一樣，對照組除了某項因素跟實驗組不一樣外，其他都要一樣，

才能證明某項因素造成差異