【快看到我看到我！】真心求助两道长得相似的题目（weaken类）。。。。。。。

ihaveausdream

1. [size=14.4444446563721px]As a practical matter, the copper available for industrial use should not be thought of as limited by the quantity of copper deposits, known or unknown. The transmutation of one chemical element into another is a modern reality, through the methods of nuclear physics. Therefore, the quantity of a natural resource such as copper cannot be calculated even in principle, because copper can be made from other metals.

[size=14.4444446563721px]　　Which of the following, if true, is the strongest argument against the argument above?

[size=14.4444446563721px]　　(A) Although it is possible that additional deposits of copper will be found, geological considerations strongly indicate that they will not amount to more than a fifty-year supply.

[size=14.4444446563721px]　　(B) The production of copper from other metals in industrial quantities would be prohibitively expensive in energy and materials.

[size=14.4444446563721px]　　(C) Synthetic materials have been discovered that can serve as practical substitutes for copper in most of its uses.

[size=14.4444446563721px]　　(D) It will be impractical, in the foreseeable future, to mine any deposits of metal that may exist on the Moon or on other planets.

[size=14.4444446563721px]　　(E) Methods for estimating the amount of copper available in currently known deposits have become very sophisticated and have proved quite accurate.



2. [size=14.4444446563721px]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 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.

[size=14.4444446563721px]Which of the following, if true, most seriously weakens the argument above?

[size=14.4444446563721px](A) The drug made from ibora bark is dispensed to doctors from a central authority.

[size=14.4444446563721px](B) The drug made from ibora bark is expensive to produce.

[size=14.4444446563721px](C) The leaves of the ibora are used in a number of medical products.

[size=14.4444446563721px](D) The ibora can be propagated from cuttings and grown under cultivation.

[size=14.4444446563721px](E) The ibora generally grows in largely inaccessible places.

ihaveausdream

我不明白的是，两题选项中的B同样都是讲成本，为什么一个就正确一个就错误呢？
希望大牛帮忙解救。。。