OG-53

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53. Two decades after the Emerald River Dam was built, none of the eight fish species native to the Emerald River was still reproducing adequately in the river below the dam. Since the dam reduced the annual range of water temperature in the river below the dam from 50 degrees to 6 degrees, scientists have hypothesized that sharply rising water temperatures must be involved in signaling the native species to begin the reproductive cycle.
Which of the following statements, if true, would most strengthen the scientists’ hypothesis?
(A) The native fish species were still able to reproduce only in side streams of the river below the dam where the annual temperature range remains approximately 50 degrees.
(B) Before the dam was built, the Emerald River annually overflowed its banks, creating backwaters that were critical breeding areas for the native species of fish.
(C) The lowest recorded temperature of the Emerald River before the dam was built was 34 degrees, whereas the lowest recorded temperature of the river after the dam was built has been 43 degrees.
(D)Nonnative species of fish, introduced into the Emerald River after the dam was built, have begun competing with the declining native fish species for food and space.
(E) Five of the fish species native to the Emerald River are not native to any other river in North America.

由题意选出关键词 temperatures 和reproductive可选出正确答案A，但从OG的解释却不求甚解，For the hypothesis to be tenable it is important that the fish in streams in the Emerald River area that retain a wide temperature difference have not lost their ability to reproduce. Choice A asserts that these fish could still reproduce and is thus the best answer.
A项中并没有谈到temperature difference 的问题啊，本题的逻辑推理到底是什么呢?

[此贴子已经被作者于2005-4-12 14:27:38编辑过]

gening

原文说annual range of water temperature in the river below the dam变了,所以科学家假设如果要重新使鱼reproduce,就必须使annual range of watertemperature恢复到原来的水平.  如果我们对比side stream of theriver里的鱼和大坝下面的鱼,发现side stream ofriver里的鱼reproduce的很好,而两个水域的一个重要差别就是water temperature不同.所以我们有理由相信恢复watertemperature到原来的水平有利于恢复鱼的reproduce.