问题
选择题
——Why is the classroom so dirty?
——Sorry, Sir. It _____ yesterday. We forgot to do it.
A．doesn’t clean
B．didn’t clean
C．isn’t cleaned
D．wasn’t cleaned
答案
答案：D
根据句意，本题应用被动语态，即“教室被打扫”，而时间是yesterday，故用一般过去时的被动语态，选D。