GmatKiss wrote: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,

I feel that the original sentence is correct.
What's the OA and the source ?

(A) in my opinion. What's the OA?

In answer choice (A) there is a problem with modification. (A) is implying that our ancestors greatly reduced their own numbers (this is incorrect because it was the event that greatly reduced ancestors). When we have an independent clause followed by a participle phrase (one that starts with a gerund and serves as an adjective clause), the participle phrase modifies the subject of the sentence.

In non-grammarese: 'ancestors' is the subject of the independent clause, 'at some time...' and because of the comma after event, we have the incorrect meaning. It was not the ancestors but an event that 'reduced their numbers.'

Therefore, we want to make sure that it is clear that 'event' is 'greatly reducing the numbers.' One way to fix that is by using the relative pronoun 'that.' In (B), we have 'an event that greatly reduced their numbers' that does a good job of correcting the error in (A).

Therefore (B) is the answer.

Hi Chris,

Can you comment on the use of hyphen in the original sentence?
Does the underlined portion need to begin with "that" in order to maintain parallelism? (Some anthropologists believe that...that at some time in the past...)

Chris, can you please explain why D is wrong? Because of passive voice?