Mike@Magoosh wrote:

Crystal W wrote:Digging in sediments in northern China, scientists have gathered evidence suggesting that complex life-forms emerged much earlier than previously thought.
This is the right sentence, but I am confused about the explanation of OG. In this Choice, OG said "It also uses a parallel active form of the verb emerge, and does not use redundant material." However, I believe here emerged is active voice but thought is passive voice. Is that OK to parallel an active voice and a passive voice?
Thanks in advance!

Dear Crystal W,
I'm happy to respond.

Folks often misunderstand Parallelism when they think it has to be a lockstep pattern of exact matching. You see, parallelism is not primarily a grammatical form: it is primarily a logical form, and grammar merely serves to indicate the underlying logical relationship. It is a profound misunderstanding to think that the two branches of parallelism have to be aligned with military conformity.

If two verbs are in parallel, they can be different tenses, or one can be active and one passive, or one could be indicative and one subjunctive. As long as the logic is clear, the details of the verb form are irrelevant. Here are a couple blogs you may find helpful:
1) GMAT Grammar Rules: Parallelism and Verb Tenses
2) Dropping Common Words in Parallel on the GMAT

Does all this make sense?
Mike