问题补充：
--- Hi, Lucy．Do you know where Linda is?
--- She in the library．I saw her there just a few minutes ago．
A. shall be
B. must be
C. should have been
D. might have been
答案：
A. shall be
(答案→)B. must be
C. should have been
D. might have been
解析：考查情态动词must表推测的用法。must + do表示对现在事情的推测。所以选B。
