Salt deposits and moisture threaten to destroy the Mohenjo-Daro excavation in Pakistan, the site of an ancient civilization that flourished at the same time as the civilizations in the Nile delta and the river valleys of the Tigris and Euphrates.

(A) that flourished at the same time as the civilizations
------ this one is good.

(B) that had flourished at the same time as had the civilizations
------ too much redundant stuff in the sentence.

(C) that flourished at the same time those had
------ unclear what that refers too

(D) flourishing at the same time as those did
------ flourishing is progressive - its incorrect. it should be flourished.

(E) flourishing at the same time as those were
------ flourishing is progressive - its incorrect. it should be flourished.


(A).

I hope that helps!

IMo A

very good question.

A : correct Idiom : same x as Y.

B : no need of past perfect. There is only 1 past event, simple past is required.

C : that flourished at the same time those had : 'as' is missing - same time as

D, E : flourishing is an present participle. Present participle takes its verb from the main clause. Here main clause is in simple present. So flourishing is representing a present ongoing event : Hence wrong