In the years 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 the 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 increases 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.
这道题我想的不是很明白：
逻辑链为：
tax涨8分钱，sales掉10%，而前一年sales掉1%。结论：销量和涨价后的价格是强相关的。
我选的B，因为我觉得如果sales和价格正相关，则去年tax涨少于8分钱，所以销量-1%，小于10%，所以tax和sales减少成正比。
但是答案为D。谁能帮忙解释一下，谢谢! | 
