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
本句子考察的是一般过去时的被动态，其结构主语+was/were+动词过去分词，根据中的yesterday，可推知。