判别充分必要与因果，请教对Lawyer方法熟悉的NN们一道OG12题：）

alvinzqn

lawyer曾提到过，因果关系和充分必要关系是完全不同的关系，没有交集。前者是一件事的发生导致另一件事的发生，时间上有先后，没有推理关系。后者是一件事的发生表示另一件事过去，现在或将来的发生，时间没有先后，有推理关系。
OG12 cr 23
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 5000 trees 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.
OG分析如下：
Situation:  The extinction of the rare ibora tree is inevitable if production of an effective infection-fighting drug continues.
如OG分析看，此题的结论是属于条件型结论，但从原文分析时，因有A lead toB, 我总觉得结论是因果型结论。对于正确选项D，应按什么思路来分析呢？对于C、E，应按什么思路排除呢？
先谢谢：）