备考2017:2017年托福写作专项模拟题(4)

托福考试网 鲤鱼小编 更新时间:2017-04-21

   Inthe listening material, the professor made several points about the invasion ofthe zebra mussels can be stopped.
  Firstof all, the reading passage states that the human transportation will cause theinvasion of the zabra mussels, while the professor contradicts that people cannotcontrol it in the past because of the lack of the knowledge. On the other hand,the ocean water will be taken by the ship to replace the freshwater, which maykill the mussels.
  Moreover,the reading passage also mentions that if the mussels are taken to the newplace, they won't have predators, while the professor refutes that they candominate it just for a short time. They will be a new food source for birds, sothey can not dominant in the end.
  Furthermore,the reading passage then talks that the invasion of the mussels will cause thedecline in the fish population in its area, while the professor departs from itthat it is true that mussels have negative impact in plankton. But for otherfish, mussels provide nutrition for fish at the bottom of the lake.

  Thisis the entirely opposed to the writer's expectation. 

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