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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.
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,
我选的是D 但我想知道为什么-———— 后面 要加that 从句 ? 这是起什么作用的?
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