GWD 3 Q4急求讲解，谢谢大侠了！！

MichelleLXN

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?

A 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.
B The one percent fall in cigarette sales in the year prior to tax increase was due to a smaller tax increase.
C The pretax price of a pack of cigarettes gradually decreased throughout the year before and the year after the tax increase.
D 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.
E As the after-tax price of a pack of cigarettes rises, the pretax price also rises.   Answer: d

我选A了，我是这样想的：如果pretax price上升了的话，即使tax不增加，aftertax price也会上升，则sales也会减少，就说明sales的减少不一定是tax影响的了，所以必须保证pretax price没有增加才说明sales下降与aftertax price的增加有关系啊？
急求哪位大牛帮忙讲解一下，谢谢了！！

MichelleLXN

额，哪位高手帮帮忙呗，马上就快考试了