问题补充:
— Theressomeone knocking on the door. Who it be?
— It must be Mary. She promised to be here at 8:00.
A. must
B. need
C. shall
D. Can
答案:
A. must
B. need
C. shall
(答案→)D. Can
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D。
考点: 考查情态动词的用法。