求助 陈向东GRE GMAT LSAT 逻辑推理题目请教

ping0114

陈向东GRE GMAT LSAT 逻辑推理题目 CH1 #21

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.

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 increase 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.

答案为E,不明白为什么选E,E不是weaken?  

请高手给个指引,万分感谢!!

robertchu

It's a supply / demand issue: the price of a goods is determined by the supply and demand of the goods.  

To see why E is a necessary assumption, we can try deny test.  Deny E, we get "A drop in demand for most illegal drugs in 1987 was the sole cause of  the drop in their wholesale price."  If so, the author's argument that the drug entry control program was a failure -- i.e., drug supply increased  --- will fall apart.  Therefore, E is a necessary assumption for the argument.

ping0114

谢谢