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.
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 LACE>LACENAME>EmeraldLACENAME> LACETYPE>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------ | 
