—________ I swim here?
—I’m sorry. Children _______ swim alone here.

Food safety is important. Rules        to stop people from food pollution.

The magazine        be Lily’s, for we can find her name on the cover.

The pollution problem here seems to get more and more serious .Something ____with it .

— There is somebody at the door. ________ it be Tom?
— No, it _______ be him. It’s just six o’clock. It’s too early.

---What should we do first if we want to develop our village?
---Lots of new roads ________, I think.
A. must built           B. can build            C. must be built

--Listen! Is Tom singing in the room? 
-- No, it ______ be Tom. He has gone to Paris.
A. mustn’t        B. needn’t        C. can’t    

--______ we clean the classroom at once?
--No, you _____. You____ clean it after school.

- You’d better           because you have to drive back home.
- OK.

- Must I clean the Lable now?
- No, you ____.  You may do it later.