Someone is knocking at the door. It     my sister. It's time for her to be back.

— Someone is knocking at the door. Is it Ann?

— It _____ be her. She is giving a performance at the theatre now.

A. may              B. must            C. can’t            D. mustn’t

--Listen! Someone is knocking at the door. Who _____it be?

---It_____be Tom. He phoned to visit me this evening.

A.may;may       B.may;shouldn’t    C.must;can      D. must;may

Someone is knocking at the door. It     my sister. It's time for her to be back.

A．can’t be         B．may not be        C．must be           D．mustn’t be