2009 进军美利坚作文组 wondersmiths2第十九次作业 9.7

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高分practice 8
In the lecture, the speaker talks about the effect of importing species on local system. She strongly casts doubts on the arguments stated in the reading passage, due to the following reasons.

First, it is true that some introduced species have stronger competitiveness for food and accommodation, but no strong evidence shows that importing species have destroyed native species. In fact, the decrease of the number of freshwater species such as frogs, salamanders, mussels and crayfishes in North America mostly results from pollutions and diseases. So, this is a direct contrast to the view displayed in the reading passage.

Second, the fact that cane toads' destructive behavior have upset the delicate ecological in Florida does not sufficient to prove that the imported species can upset the ecological balance of a region. In contrast, the cane toad is an exception. Mostly under right control, the imported species can benefit the local system such as agriculture and scientific research. Hence, we cannot conclude the point that the ecological balance of a region will be upset by the imported species like the reading passage.

Finally, the speaker points out that mesquite trees actually have brought economic gain to local system for the reason that they provide shelters and food for bird and animals and also can be used in agriculture and as fire woods for local people. Therefore, although the imported species may bring harm to some species on the region, they can benefit the economy of the region as a whole.