68、A drug that is highly effective in treating many types of infection can, at present, be obtained only from the bark of the ibora, a tree that is quite rare in the wild. It takes the bark of 5,000 tree to make one kilogram of the drug. It follows, therefore, that continued production of the drug must inevitably lead to the ibora’s extinction.

Which of the following, if true, most seriously weakens the argument above?

(A) The drug made from ibora bark is dispensed to doctors from a central authority.

(B) The drug made from ibora bark is expensive to produce.

(C) The leaves of the ibora are used in a number of medical products.

(D) The ibora can be propagated from cuttings and grown under cultivation.

(E) The ibora generally grows in largely inaccessible places.

答案是D。

我做的时候在D和E中间犹豫了很久，虽然最后还是选了D，但是总觉得E项也可以weaken该结论呀。既然都已经说了ibora长在inaccessible的地方，那么就应该是inaccessible的，这样就不会导致灭绝了呀。

而OG给出的解释说if the ibora is largely inaccessible (choice E), this bears on the question of whether production of the drug could continue, not on what would happen if it did continue，即该项只能推出生产是否能继续的问题，而不是如果继续的话将会怎样的问题。

不是很明白，谁给说说呀。

我的想法是：E看起来对，但它其实不对。大大的不对。inaccessible是指很难或根本达不到。“hard or impossible to get to or get at”。请看当今世界上最权威的美国词典Merriam-Webster online thesaurus: http://www.m-w.com/cgi-bin/thesaurus?book=Thesaurus&va=inaccessible

所以说它有可能是可以达到的。

文章的推理过程是：drug的生产需要大量的ibora。所以drug的生产会导致ibora的绝种。

暗含的假设是：ibora本身数量不会增加。

而D选项正是这个假设取非，所以正确。

E是说drug本身就不能生产，反对前提，而不是针对推理过程或是结论，所以错。

等待NN指教~~~

that continued production of the drug must inevitably lead to the ibora’s extinction中，continued production是前提，问题是：如果持续生产，将导致灭绝。weaken的方向应该是：即使持续生产，也不会导致灭绝。必须承认出题者的前提。E项反对的是前提，所以不对。