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. A (E) Five of the fish species native to the Emerald River are not native to any other river in North America. 答案是A。 谁能解释一下结论?scientists have hypothesized that sharply rising water temperatures must be involved in signaling the native species to begin the reproductive cycle. OG的解释: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. 前提说none of the eight fish species native to the Emerald River was still reproducing adequately,也就是reproduce不够,而不是不能reproduce,那为什么A中说reproduce only in side streams,这不是说在6 degrees的时候不能reproduce,与结论矛盾了吗?如何支持结论呢?  
[此贴子已经被作者于2006-9-5 22:05:31编辑过] |