问题
选择题
--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
答案：C
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。
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