2018年6月六级真题(第二套)

Questions 16 to 18 are based on the recording you have just heard.

Directions: In this section, you will hear three recordings of lectures or talks followed by three or four questions. The recordings will be played only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C) and D). Then mark the corresponding letter on Answer Sheet 1 with a single line through the centre.

    16.
  • A They will root out native species altogether.
  • B They contribute to a region's biodiversity.
  • C They pose a threat to the local ecosystem.
  • D They will crossbreed with native species.
    17.
  • A Their classifications are meaningful.
  • B Their interactions are hard to define.
  • C Their definitions are changeable.
  • D Their distinctions are artificial.
    18.
  • A Only a few of them cause problems to native species.
  • B They may turn out to benefit the local environment.
  • C Few of them can survive in their new habitats.
  • D Only 10 percent of them can be naturalized.