「Question No. 84」

　　The following is a letter to the editor of an environmental magazine.

　　“Two studies of amphibians in Xanadu National Park confirm a significant decline in the numbers of amphibians. In 1975 there were seven species of amphibians in the park, and there were abundant numbers of each species. However, in 2002 only four species of amphibians were observed in the park, and the numbers of each species were drastically reduced. One proposed explanation is that the decline was caused by the introduction of trout into the park's waters, which began in 1975. (Trout are known to eat amphibian eggs.)”

　　Instructions:

　　Write a response in which you discuss one or more alternative explanations that could rival the proposed explanation and explain how your explanation(s) can plausibly account for the facts presented in the argument.

　　Introduction

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　　Body

　　Alternative explanation 1:

　　Trout may not have been the reason why there are reduced numbers of each species and fewer species. An alternative explanation is as follows: some of the “missing” species may have failed to adapt to the climate change, which is possible during the roughly thirty years’ time, and died, or the park’ environment had changed during the years, and some of the species may have migrated to the outside of the park for places that are more habitable. In this case, those amphibians may have died or have moved out of the park before trout had a chance to eat their eggs.

　　Alternative explanation 2:

　　Second, it is not unlikely that the park had a reduced area in 2002, when researcher counted the species and the numbers of species. In this case, the missing species may have remained where had always been but would not have been counted as park’s species. As a matter of fact, if the shrinkage of area took place in 1975, trout would not even have had a chance to eat the eggs of some of the amphibians’ eggs.

　　Alternative explanation 3:

　　Third, humans may be another factor, since there may have been poachers, who hunt amphibians. If humans’ poaching had taken those “missing” species before the trout had a chance to eat amphibians’ eggs, trout should be ruled out as a factor.

　　Alternative explanation 4:

　　提示：Based on the information that “only four species of amphibians were observed in the park”, we know that observation is the way of counting the numbers. It is therefore likely that the observation may be inaccurate. Blah blah blah。

　　其它可能的逻辑点：略

　　Conclusion

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