GMAT Sentence Correction (SC) | Re: Some anthropologists believe that the genetic homogeneity

Some anthropologists believe that the genetic homogeneity evident in the world's people is the result of a "populationbottleneck"—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- correct


B that at some time in the past our ancestors