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[Sentence Correction]
试题详情
题目：
Some anthropologists believe that the genetic homogeneity evident in the world's people is the result of a "population bottleneck"—at some time in the past our ancestors suffered an event, greatly reducing their numbers and thus our genetic variation.
选项:
A、at some time in the past our ancestors suffered an event, greatly reducing their numbers
B、that at some time in the past our ancestors suffered an event that greatly reduced their numbers
C、that some time in the past our ancestors suffered an event so that their numbers were greatly reduced,
D、some time in the past our ancestors suffered an event from which their numbers were greatly reduced
E、some time in the past, that our ancestors suffered an event so as to reduce their numbers greatly,
答案:
B
提问：
错选D。不知道怎么判断出需要保留that和at呢？我把D选项理解成some time in the past（when省略） our ancestors...所以刚开始就把ABC三个有介词的选项直接排除了。
解答：
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