Do you think it’s a good idea to make friends with your students?– _____ , I do I think it’s a great idea

下列各句中，加线的成语使用不恰当的一句是(　　)

He must be helping the old man to water the flowers,______ ?

It’s 7o’clock. Tom___________ dinner at home.

Are you sure you have to do this now It’s been very late.—I don’t know to do it if not now.