[讨论] 天山真题一道

GeorgeWBush

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.
答案为什么是D呢？麻烦哪位解释一下，谢谢！

usdusaj

the pretax price in the privious year a1+t1
the pretax price in last year            a2+t2
here a is after tax price, t is tax
here t2--t1=0.08
if a2+t2-a1-t1<=0.08, then a2--a1<=0, the after tax price in last year is cheaper than privious year.  y will it become a concern for customers to buy cigarettes? so it has no relation with the after-tax price of a pack of cigarettes.

GeorgeWBush

明白了，多谢usdusaj兄。不过这更象一道数学题。