--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
网友回答
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。