2. 外语
  3. Scientists formerly assumed that coral populations remained stable, dead polyps being replaced by now ones that build on the "sk

Scientists formerly assumed that coral populations remained stable, dead polyps being replaced by now ones that build on the "sk

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问题     Scientists formerly assumed that coral populations remained stable, dead polyps being replaced by now ones that build on the "skeletons" left behind. Recent investigations, however, reveal more dynamic processes. Whole sections of a colony may die and not be replaced. This process, known as partial colony mortality, is evident in a series of photographs over time, but often impossible to detect in site because "skeletons" bared by the death of overlying tissue are readily overgrown by other organisms or abraded by grazers. Partial mortality can produce fission the process of a large colony splitting apart into two or more adjacent colonies that presumably have identical genetic makeup. Subsequent lateral growth may unite these colonies in a process called fusion. As a consequence of these three processes, estimates of coral ages based on size are Partial mortality and fission, which reduce colony size, occur more frequently than fusion, and thus estimates of coral age based on colony size are probably far too low.
The primary purpose of the passage is to______.
选项 A、explain the fission and fusion processes that have considerable effect on the life expectancies of coral populations
B、point out the major differences between the three dynamic processes by which coral colonies grow and maintain themselves
C、explain the various dynamic processes undergone by coral colonies which make estimating their ages difficult
D、explain the effects of partial mortality on fission and fusion processes in coral colonies
答案C
解析 主旨大意题。文章的主旨在于介绍珊瑚礁所可能经历的三种进程，即死亡、分裂和融合，并进而指是由于存在这三种进程，才使得对珊瑚礁年龄的估测变得困难。故C选项符合文意。
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