OG-53

peeeepy

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.

刚开始做的时候选对了，后来对答案时又觉得不对，因为看到了那个only,题干上是说那些鱼不再adequately reproduce, 那就是说还可以繁殖，只是不像以前那样繁殖的多了，我觉得能够加强这个结论的条件应该是说在没有dam的时候，或者说在温度range正常的情况下，鱼能够adquately繁殖，可是答案中却说鱼 reproduce only in side streams of the river below the dam where the annual temperature range remains approximately 50 degrees.觉得逻辑不对，so confusing....

看了OG的解释和以前的讨论，还是没搞明白，第一次在这里问问题，想把问题问清楚也不容易，希望大家能看明白：）

babypace

I think A is the only choice, all the other anwers have nothing to do with the hypothesis.

The fishes can't reproduct adequantly because of the temperature change of the water. A gives a situation to compare that if the temperature of the water keeps at 50 degrees, the fishes still can reproduce. "Only" indicates the specific area with the temperature apppro. to 50 degrees, but not any OTHER temparature areas.

A points out the relationship between the temperature and the productivity of the fish in the river.

[此贴子已经被作者于2005-6-11 12:05:12编辑过]