[求助]问一道题的思路，觉得自己的想法好怪：（

The program to control the entry of illegal drugs into the country was a failure in 1987. If the program had been successful, the wholesale price of most illegal drugs would not have dropped substantially in 1987.
13. The argument in the passage depends on which of the following assumptions?
(A) The supply of illegal drugs dropped substantially in 1987.
(B) The price paid for most illegal drugs by the average consumer did not drop substantially in 1987.
(C) Domestic production of illegal drugs increased at a higher rate than did the entry of such drugs into the country.
(D) The wholesale price of a few illegal drugs increased substantially in 1987.
(E) A drop in demand for most illegal drugs in 1987 was not the sole cause of the drop in their wholesale price.

答案是e.题目说如果控制非法药物进入失败了。如果成功，非法药物的价格就不会下降。换句话说，就是现在因为失败药物价格下降了。用取非削弱判断，，e,如果需求的下降是唯一原因，则题目不成立。所以e所说的“其他原因”就是供给的增加。

是这样的么？觉得自己现在思路太混乱了……

GG总结的完全正确,正因为需求的下降不是导致价格下降的唯一原因,所以才可以有题中的推理

这是道典型的排除它因题. 题中说A-B,假设就是C不能推出B(或C也能推出B但并不是唯一能推出B的,充分而不必要)