问题
选择题
— Must they clean and tidy the classroom now?
— No, they . It after school in the afternoon.
A．mustn’t; must clean
B．needn’t; must clean
C．mustn’t; need be cleaned
D．don’t have to; can be cleaned
答案
答案：D
must构成的一般疑问句通常否定回答时用needn’t或don’t have to，本题的最后一句是被动句，结构为be+过去分词，即be cleaned，故本题选D。