问题补充:
—Theres someone knocking on the door.Whoit be?
—It must be Mary.She promised to be here at 8:00.
A. must
B. can
C. shall
D. need
答案:
A. must
(答案→)B. can
C. shall
D. need
解析:句意:--有人在敲门。可能会是谁呢?--一定是Mary。她答应八点钟到这里。A. must一定,表主观肯定推测;B. need需要;C. shall将会是;D. can可能,表示怀疑、猜测、惊异(主要用于否定句或疑问句中)。故选B
考点: 考查情态动词的用法。