–Our classroom twice a day. So it is very clean.
–It is important for us to do this.
A. is sweeping
B. is swept
C. sweeps
D. has swept
网友回答
A. is sweeping
(答案→)B. is swept
C. sweeps
D. has swept
解析：句意：我们的教室一天打扫两次。所以它很干净。对我们来说打扫教室很重要。根据句意，可知句子要用被动形式，本题中说明的是一般的情况，故用一般现在时的被动，故选B