—Listen! There is a knock on the door. Who it be?—It must be Jack. Just now I sent for hi

问题补充：

—Listen! There is a knock on the door. Who it be?

—It must be Jack. Just now I sent for him.

A. shall

B. can

C. must

D. might

答案：

A. shall

(答案→)B. can

C. must

D. might

解析：考察情态动词，四个选项在第三人称后分别表示会；应该、能、一定必须和可能。might语气比can弱。在表示猜测的时候，might用于肯定推测，can用于否定推测。根据题意选B，他能是谁呢？