og-53，以前没有链接的

omeimei

53.

Two decades after the Emerald River Dam was built, none of the eight fish species native to the laceName>EmeraldlaceName> laceType>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>EmeraldlaceName> laceType>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>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.

53.

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.

Choice B undermines the hypothesis by suggesting a completely different hypothesis; choice C tends to support the claim that the temperature variation has lessened but does not show that this is the right explanation; 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; and choice E emphasizes the seriousness of the problem but sheds no light on what causes it.

这题的答案没问题，我考虑的是：排除掉温度变化的情况，说明只要温度回来鱼就可以繁殖。

可是我看答案说的（加黄底色）好像又不是那么回事，是我想错了吗？

谢谢了哦。

babypace

这题选A提供了科学家假设成立所必需的前提，就是鱼类没有失去自身的繁殖能力。 A说了在50度水域，鱼还是照常繁殖的。 如果A不成立，就是说鱼类自己的繁殖能力没有了，那么假设中说的温度升高，鱼也不会回复到从前的繁殖率的。所以A支持了科学家的假设，而且是假设成立的必要条件。

omeimei

谢谢哦。