—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
网友回答
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？