L2004-12-1-12

12.     Biologists have noted reproductive abnormalities in fish that are immediately downstream of paper mills. One
possible cause is dioxin, which paper mills release daily and which can alter the concentration of hormones in   fish.However, dioxin is unlikely to be the cause, since the fish recover normal hormone concentrations relatively quickly during occasional mill shutdowns and dioxin decomposes very slowly in the environment.

           Which one of the following statements, if true, most seriously weakens the argument?

(A) Some of the studies that show that fish recover quickly during shutdowns were funded by paper manufacturers.
(B) The rate at which dioxin decomposes varies depending on the conditions to which it is exposed.
(C) Normal river currents carry the dioxin present in the river far downstream in a few hours.
(D) Some of the fish did not recover rapidly from the physiological changes that were induced by the changes in   hormone concentrations.
(E) The connection between hormone concentrations and reproductive abnormalities is not thoroughly understood.

答案是(c),怎么看也没能看出来.不知道大家是怎么来理解的.总觉得无法 weaken.挠头挠头....

Hmm, more complicated than this

1) and 2) together is saying there is cause(doxin even though occassional shutdown) but no effect. So doxin is not cause.

C) shows when mill shuts down, there is actaully no doxin because the released ones have been all carried away.