The room is very clean because it()by us

问题描述:

The room is very clean because it()by us
was kept
is clean
is cleaned
will be swept
说下原因谢谢了

is cleaned .从前面的is可以判断是现在时,所以是is,由于by us可以知道是被动语态,所以是选一个动词的过去分词.