--Listen! Someone is knocking at the door.

-- ______ be Mary. She has just been to Beijing

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

---Listen!Someone is knocking at the door．

--- ________ be Mary．She has just been to Beijing

1. A.
   She mustn’t
2. B.
   It can’t
3. C.
   It must
4. D.
   She may

-Listen, someone is knocking at the door?

-Who can ________ be?

1. A.
   he
2. B.
   it
3. C.
   she
4. D.
   this

－Listen, someone is knocking at the door?

－Who can ________ be?

[　　]

Listen！Someone is knocking at the door．

________ be Mary．She has just been to Nanjing．

[　　]