请教OG 53!

northeuro

Two decades after the Emerald River Dam was built, none of the eight fish species native to the laceName w:st="on">EmeraldlaceName> laceType w:st="on">RiverlaceType> 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 laceName w:st="on">EmeraldlaceName> laceType w:st="on">RiverlaceType> annually overflowed its banks, creating backwaters that were critical breeding areas for the native species of fish.

(C) The lowest recorded temperature of the laceName w:st="on">EmeraldlaceName> 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.

答案是A，我是按照无关选项的方法排除其他的，但是仍然不明白在大坝下支流中幸存的鱼群怎样支持了原文中的假设？

还请NN指教

bigmouse

请先到置顶的《讨论汇总》中看看有没有人讨论过相同的问题～～～

另外浏览置顶的《发贴必读》，注意发贴格式～～～

谢谢对CD的支持～～～

sweetstar

问同一题，请NN回答。

在置顶贴里没有发现此题。

NIRVANA050504

已知：无法繁殖，温度下降

推测：温度下降导致无法繁殖

假设：升高温度能解决问题

A: 在原先的温度下，繁殖正常。正好能支持假设，只要恢复温度就能解决问题；

B: 它因，明显weaken；

C的lowest temperature, D,E的nonative species 应该都属无关吧。

qwyang

已知：无法繁殖，温差被从50减小到6，即温度升高了

推测：温差下降导致无法繁殖

假设：升温对繁殖有影响

A: 在原先的温差下，繁殖正常。正好能支持假设，升温对繁殖有影响；

B: 它因，weaken；

C D,E无关

请牛牛指点

annali

举事实直说

steveyangxt

表明温度是唯一的影响因素， 所以加强原文。