they often clean their classroom often school =they classroom____often____by them?

问题描述:

they often clean their classroom often school =they classroom____often____by them?

is; cleaned
因为classroom作主语,often用于一般现在时中,必须用一般现在是的被动语态,所以是is cleaned
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they often clean their classroom often school =they classroom____often____by them?
The\Their classroom is often cleaned by them.
be+过去分词表被动

is; cleaned