--Listen! Someone is knocking at the door.-- be Mary. She has just been to BeijingA. She

问题补充：

--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

答案：

A. She mustn’t

B. It can’t

(答案→)C. It must

D. She may

解析：此题充分体现了一题多考点的命题倾向，考查了情态动词的选择，代词的选择以及隐含语境has been to的用法。