2. 考研
  3. A. help maintain environmental quality B. as people clear lands C. depends on countless interactions D. by overfishing and by po

A. help maintain environmental quality B. as people clear lands C. depends on countless interactions D. by overfishing and by po

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问题 A. help maintain environmental quality
B. as people clear lands
C. depends on countless interactions
D. by overfishing and by pollution Phrases:
A.【T13】________for homes and farms and cut wood for fuel
B. They also【T14】________by breaking down or removing some pollutants
C. fish supplies have been greatly reduced【T15】________
D. 【T16】________among plants, animals, and microorganisms
    Wildlife plays a vital role in the biological processes that are essential to life itself. The functioning of the biosphere, and hence the maintenance of human life,【T17】________These processes are essential for agriculture, fisheries, and other efforts necessary to human life. 【T18】________and by preventing the pile-up of waste. Some of the biological processes in which wildlife is involved are seed scattering, soil generation, nutrient cycling and pest control.
    No discussion of threats to wildlife is complete without an examination of the causes, which are human needs. In Africa, forests are shrinking 【T19】________Sheep eat the vegetation, leaving the bare soil to be carried away by wind and water. Humans kill wildlife for the illegal trade in furs. The loss of forests is destructive to many species and plants. Beyond that, in the oceans, 【T20】________.
【T18】
选项 A、 
B、 
C、 
D、 
答案B
解析 本题前句讲的是生物圈的功能及重要性，所以后面接着也可以维持环境质量。故选B。
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