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 flurished at the same time as the
civilizations
(B) that had flourished at the same time as had
the civilizations
(C) that flourished at the same time those had
(D) flourishing at the same time as those did
(E) flourishing at the same time as those were

Can somebody explain why we do not need to use a verb after as in A?