一道GWD

laila11

Parland’s alligator population has been declining in recent years, primarily because of hunting.  Alligators prey heavily on a species of freshwater fish that is highly valued as food by Parlanders, who had hoped that the decline in the alligator population would lead to an increase in the numbers of these fish available for human consumption.  Yet the population of this fish species has also declined, even though the annual number caught for human consumption has not increased.
Which of the following, if true, most helps to explain the decline in the population of the fish species?
A.    The decline in the alligator population has meant that fishers can work in some parts of lakes and rivers that were formerly too dangerous.
B.    Over the last few years, Parland’s commercial fishing enterprises have increased the number of fishing boats they use.
C.    Many Parlanders who hunt alligators do so because of the high market price of alligator skins, not because of the threat alligators pose to the fish population.
D.    During Parland’s dry season, holes dug by alligators remain filled with water long enough to provide a safe place for the eggs of this fish species to hatch.
E.    In several neighboring countries through which Parland’s rivers also flow, alligators are at risk of extinction as a result of extensive hunting.

看不明白,谁给解释一下,总觉得D会是fish数量增加啊,怎么能解释减少呢?

NicoleYu

文章首先指出了鳄鱼和淡水鱼之间的捕食关系，指出人们希望在鳄鱼减少的时候，淡水鱼能因为捕食者的减少而增加
但实际情况却不是人们希望的那样的，在人类捕鱼量没有增加的情况下，淡水鱼的数量也减少了

这里D给出了一个解释，即鳄鱼和淡水鱼之间不仅存在捕食关系，还存在共生的关系：在干旱季节，鳄鱼挖出的洞里仍然有水，淡水鱼可以在这些洞里安全的产卵和孵卵。有了这一层关系，那么随着鳄鱼的数量下降，鳄鱼挖的洞也减少了，在干旱季节淡水鱼可以安全产卵和孵卵的地方也大大减少，所以淡水鱼的数量也减少了。