53. Two decades after the Emerald River Dam was built, none of the eight fish species native to the LACE>LACENAME>EmeraldLACENAME> LACETYPE>RiverLACETYPE>LACE> 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.>>

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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.

文中说大坝使温差 the annual range of water temperature 从50度降到6度，从而导致物种难以再生，然后又说若温度升高sharply rising water temperatures 就可以使the native species to begin the reproductive cycle. 而答案A中又说是温差保持在50度--即温差升高就可以使物种再生。 此题症结在哪，那位NN帮忙解释一下，谢谢------

谢谢楼主！

但还是不明白为什么高温差=高温度

温差和温度是两个截然不同的概念啊

阅读OG解释，发现关于“most strengthen the scientists’ hypothesis”中的“the scientists’ hypothesis”OG明显是指the reduced annual range of water temperature ——〉本地鱼不繁殖，这样选A排除其他选项就没问题了

但是，如果把hypothesis的重点放在提高水温能促进鱼繁殖上，同时默认温差是促使鱼繁殖的条件，这样C选项比较合理：最低水温体高了---〉温差变小---〉提高水温促进繁殖

“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”到底怎么理解呢？请NN指点迷津

哎...sharply rising water temperatures 意思是"剧烈上升的水温",而非"大幅度升温".

本来认为文章在说: 温度范围变小了=>建议升温. 这毫无逻辑!除非建坝前range的最大值 >> 建坝后range的最大值.例如原先是0~50,现在是0~6,而那些鱼又恰恰在 6(或更高)~50 范围内繁殖. 这种情况下建议升温还能说的通.

抱着这样的想法,觉得A跟"要升温"这件事情不沾边,立马就被排除. 而C是在比较两个range的最小值,非最大值,似乎关系不大;但细看数值:建坝前是34~84,建坝后是43~49,也就是说range的最大值相差35,好象也不小.

故认为C比A更贴切.  分析得蛮有道理吧?!呵呵.估计楼主也犯了同样的错误.

但是怎样才能正确理解sharply rising water temperatures呢?

还请不吝赐教!

我觉得关键是个range这个概念,怎样理解sharply rising temp并不重要,sharply rising可以定义一个月内,也可以是一天．．．多想和深究是没必要的．

annual range在50的时候水温必定波动会大,水温的波动会给fish a signal--time to reproduce.当range在６时，基本是衡温根本不会有sharply rising的可能所以不会给鱼发出信号．