OG-53新问题, 各位NN帮忙看看啊

请各位版主帮忙解惑.

OG-53

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.

"since D relates a development after the native species began
to decline, it does not bear on the hypothesis, which concerns the decline’s original cause", 不理解OG这句话, 我觉得D是在削弱, 虽然不是那么的完美, 但是我觉得多少还是有点关系的, 为什么OG说"after the native species began to decline"然后就排除了? 我觉得如果后面加入的因素影响到reproduce, 整个的再生过程还是会受到影响的, OG的说法不理解, 请教各位NN.

请先参考下前人的讨论：

状态	标题或简要内容	作 者	发表时间	版 面
	OG-53	peeeepy	2005-6-10 0:21:46	【GMAT逻辑专区】
	OG-53	triangle	2005-4-9 14:59:21	【GMAT逻辑专区】
	og-53，以前没有链接的	omeimei	2005-1-14 1:36:00	【GMAT逻辑专区】
	og-53;og-54	david_348	2004-10-23 22:43:41	【GMAT逻辑专区】
	OG-53	wwwhahchn	2004-10-21 23:15:42	【GMAT逻辑专区】
	OG-53	axbycd	2004-7-3 9:34:10	【GMAT逻辑专区】
	OG-53	axbycd	2004-6-24 7:02:28	【GMAT逻辑专区】

nonnative的引入会和"本地鱼"强吃的, 虽然没有必然的逻辑关系说明这样会导致再生能力的下降, 但是我觉得至少不可以说一点影响都没有.

当然这个选项本身是不好的, 但是不理解为什么OG会说since D relates a development after the native species began to decline, it does not bear on the hypothesis, which concerns the decline’s original cause, 就像我刚刚说的, 后加入的因素也可能会造成影响的.

PS. 说法比较土, MM见谅.

我大概了解你说的意思: nonnative fish争食造成本地鱼生存困难
站在猜想ETS的想法上,
1) Choice D 中出现 declining native fish. 似乎暗示是native fish are declining, 源头的因不是nonnative fish
  (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)

2) 就如OG针对D的解释, nonnative fish是后来的因素(你也认同这个看法), 的确会造成影响后来native fish的生存, 可能让native fish进一步减少, 加重问题的严重性。

    所以应该这么说, 你的认知没有错, 也和OG的解释一致, 都是发展后来的因素, 当然对native fish生存有影响(他因), 但是时间点和本题主要的逻辑线不一样:

   水坝建立--> 温差变小--> 没有急遽上升温度讯号--> native fish无法正常繁殖

这个说法我很赞同, 从时间上面说, 的确不是造成问题的根源, 但是即使不是, 现在存在的问题仍然可以导致最终reproduce的不成功, 我觉得OG这里说的有问题, 如果它说: 文章没有"the intruduction of nonnative fish"和"declining reproducing ability"的逻辑联系, 所以是out of scope.

我觉得我就没有话说了, 但拿个时间顺序来解释我觉得不可以接受, MM看法呢?

关于时间的前后顺序说法…恩…这点我觉得是ETS惯用回答的方式之一,
(Sorry 一时之间 想不出来哪题举例 等我找到再po上来)

我想这也是为什么 很多人很难接受CR的解释原因之一
常常可以用out of scope 快速排除的选项, ETS解释仍然会说此选项和题目有什么关系之类的
因此 读CR解释 有时候是挺难受的
当然这是我个人的观点

我想你的说法是OK的, 直接把两者因果逻辑关系否定, 所以Choice D是out of scope.
能正确快速的排出这个答案应该是最重要的吧