OG11-75 as后面是否要补动词？

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

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

答案是A，但是as不是后面跟句子吗？OG里一提到as就说后面要有clause, (subject and verb)，为什么这里没有动词呢？请高人指教！

这个题目的关键是习惯用语和一致性：

习惯用语：the same ...as；

一致性：an ancient civilization...the civilization。

翻译：盐分堆积和湿气可能毁坏巴基斯坦地区的出土文物，该地区的古文化曾与同时期的尼罗河三角洲和底格里斯河和幼发拉底河附近平原上的古文化共同繁荣。