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2013年GMAT考试最新逻辑推理试题训练十五 查看汇总：2013年GMAT考试最新逻辑推理试题训练汇总 1. 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.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. 2. High levels of fertilizer and pesticides, needed when farmers try to produce high yield of the same crop year after year, pollute water supplies. Experts therefore urge farmers to diversify their crops and to rotate their plantings yearly.To receive governmental price-support benefits for a crop, farmers must have produced that same crop for the past several years.The statements above, if true, best support which of the following conclusions? | 
