—Who it be that is knocking at the door?—It be Father but I’m not sure.A. can; mustB. ca

问题补充：

—Who it be that is knocking at the door?

—It be Father, but I’m not sure.

A. can; must

B. can; may

C. must; can

D. may; must

答案：

A. can; must

(答案→)B. can; may

C. must; can

D. may; must

解析：考查情态动词。第一句话：可能是谁在敲门？是一个强调句型的特殊疑问句。It can be …..that….。第二空是情态动词表示推测，后半句有but I’m not sure，说明不确定，应该用may.所以选择B。