问题补充:
——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:
A. doesn’t clean
B. didn’t clean
C. isn’t cleaned
(答案→)D. wasn’t cleaned
解析: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。