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？
水温上升可以使得生育步入正轨（若要开始新的一轮生育，则必须提高水温）
现象，dam降低水温－－生育不足
假设：如果提高温度－－生育重新开始不如正轨
A说的确是在50度左右,鱼有能力生育。符合scients的hypothsis
不好意思，没搞懂，继续请教。
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.
大坝建好后，8中当地的鱼生育不足。
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.
原因：大坝减少河水的温差，从50度到6度，
于是科学家假设:上升的水温意味着本地鱼开始生育。问题是问支持假设。
(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.
A说本地鱼还能在大坝下支流中温差在50度的水中生育。
首先这个问题有些tricky。annual range of water temperature缩短不等于temperature升高，如果range [-30,20]，[-30,-24]。
其次，A说本地鱼还能在大坝下支流中温差在50度的水中生育，这和结论上升的水温意味着本地鱼开始生育无关呀，又没说本地鱼可在温差在6度的水中生育？如果把结论改为上升的水温限制了本地鱼生育，好像还有道理，因为生育不足吗。
苹果斑竹，帮忙在解释一下。谢谢。
再顶！
我的理解是水温的范围从50左右下降到6度左右
A说支流里的水温范围接近50度左右，且仅在这个范围里鱼才能生育
我对这句话不太理解：sharply rising water temperatures must be involved in signaling the native species to begin the reproductive cycle.
上升的水温是一个信号，预示着本地鱼开始生殖周期？生育不足还是足够？
我的推理：
大坝修好--〉本地鱼生育不足。
大坝修好--〉水温差减小。
假设：水温上升--〉本地鱼开始生育
问支持假设？
A是本地鱼在水温差大的地方还能生育。
怎么支持呢？有点卡住了！ 救命救命！！！
我对这句话不太理解：sharply rising water temperatures must be involved in signaling the native species to begin the reproductive cycle.
上升的水温是一个信号，预示着本地鱼开始生殖周期？生育不足还是足够？
－－begin the reproductive cycle
我的推理：
大坝修好--〉本地鱼生育不足。
大坝修好--〉水温差减小。
假设：水温上升--〉本地鱼开始生育
问支持假设？
A是本地鱼在水温差大的地方还能生育。
－－对A理解有误：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
A说only in side streams where temperature approximately 50度。即只有在50度的水域，才能繁殖
差点走火入魔！！！这题困扰我好几天了。两位提醒的非常对。
严重感谢。
送花！
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