'as'

[bids77]

Q. Salt deposit and moisture threaten to destrom the Mohenjodaro excavation in Pakistan, the site of an ancient civilization that flourished at the same time as the civilizations in the Nile delta.

OA is A, means the sentence is correct. But I think there is the error of parallelism in the sentence. The sentence should be like this -
.....that flourished at the same time as did the civilizations in Nile delta.
Please explain..

[RonPurewal]

Q. Salt deposit and moisture threaten to destrom the Mohenjodaro excavation in Pakistan, the site of an ancient civilization that flourished at the same time as the civilizations in the Nile delta.

OA is A, means the sentence is correct. But I think there is the error of parallelism in the sentence. The sentence should be like this -
.....that flourished at the same time as did the civilizations in Nile delta.
Please explain..

the sentence would be correct that way, too, but you don't NEED the extra 'did'.
in general, the gmat only inserts these extra helping verbs when they resolve an ambiguity in the sentence; here, there is no ambiguity, because you can't claim that the civilizations themselves are a 'time'. that leaves you with one interpretation: the M-D civilization flourished at the same time as did the other civs (without having to say 'did').

here's an example of a sentence that IS ambiguous and DOES require an extra helping verb:
i know more about shakespeare than my brother.
there are 2 possible interpretations. here are UNambiguous sentences representing each of those interpretations, with the appropriate helping verbs:
(1) i know more about shakespeare than does my brother.
(2) i know more about shakespeare than about my brother.