请各位帮忙看看这道题，我对答案有些异议：
32. 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.
划线部分是正确答案。可是根据比较从句的原则，按道理as后面的部分应该添加did，为什么这里却没有？
想听听大伙的看法。
谢谢！ | 
