问题
选择题
(2011·江西)It ________ be the postman at the door.It's only six o'clock.
A．mustn't
B．can't
C．won't
D．needn't
答案
答案：B
根据It's only six o'clock推知，那不可能是邮递员，否定形式推测要用can't或couldn't。因为must表推测时，只能用于肯定句。
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