---There is somebody knocking at the door. Who it be?---I’m not sure. It be a postman.A.

问题补充：

---There is somebody knocking at the door. Who it be?

---I’m not sure. It be a postman.

A. may; must

B. will; can

C. can; may

D. may; will

答案：

A. may; must

B. will; can

(答案→)C. can; may

D. may; will

解析：may可以，可能；must必须，一定；will将要；can能，可能。句意：有人在敲门。可能是谁？——我不确定。可能是邮递员。结合语境可知选C。