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,
题目分析：如果用A那就是ancestors做出reduce的动作了，语义不对。B是event做出reduce这个动作，语义合理，留着。C后面非得用个被动，别扭，没有B好。D和C差不多，干掉。Ereduce又是ancestors干的了，发起者不对，选B
