Before being painted pink ,the wall should be cleaned throughly 为什么being不能去掉?

问题描述:

Before being painted pink ,the wall should be cleaned throughly 为什么being不能去掉?

表被动啊,不能去过去分词,作状语时,be动词一般都要省略的呀?那都放在首句了是不是before有关,请详细解释一下。解释清楚了马上给采纳,before是介词,后面一定要跟动词ing形式。