-–Mary knows the city quite well.
--She well have been there before.
A. need
B. could
C. should
D. may
网友回答
A. need
B. could
C. should
(答案→)D. may
解析：考查情态动词：A. need 需要B. could 能够C. should应该D. may可以，几个选项只有may可以用may well do sth的意思是“有足够/充分的理由去做某事”。 句意：玛丽很了解这个城市。--她很有可能去过那里。选D。