问题描述：
----There's someone at the door.Who____ it be Is it the postman?
----No,It _____be him.It's just 7 o'clock.It' too early
A can; can't B will won't C may mustn't D may not ; must
----No,It _____be him.It's just 7 o'clock.It' too early
A can; can't B will won't C may mustn't D may not ; must
问题解答：
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