单选题 7. Princessfish are a species of coral-reef fish that are captured alive by divers who first stun the individual fish by squirting a certain poison at them. Since the divers limit their catch to a few individuals and take care not to overfish, the divers' continuing activities will clearly not result in serious harm to populations of princessfish.
Which of the following, if true, most seriously weaken the argument given? ______

A、 Princessfish cannot be captured alive by traditional methods of fishing.
B、 The poison used to stun the princessfish has no effect on humans who eat them.
C、 Demand for princessfish has remained steady during the last decade.
D、 Traces of the poison that remain in the seawater damage the Corals that create and maintain the reefs on which princessfish depend.
E、 Fish that have been stunned but have selected for capture by the divers soon recover from the temporary effect of the poison.

【正确答案】 D

【答案解析】 D：潜水员的毒药残留物破坏了公主鱼的生存环境，证明会破坏鱼群，属于“直接削弱结论”。该选项也可以看作是“寻找他因”。原文中假设导致鱼群破坏的原因只有过度捕捞，而该选项则说明，毒药残留物破坏生存环境也会破坏鱼群。
A：公主鱼是否能被传统方法活捉，与鱼群是否会受到破坏无关。
B：文章讨论的是鱼的情况，和吃鱼的人无关。
C：对于鱼的需求保持稳定，只能进一步加强潜水员不会过度捕捞，故不选。
E：鱼会从毒药的效果中恢复过来，进一步加强说明鱼群没有遭到破坏，故不选。