问题补充：
– Mary was crying sadly.
-- Oh, she the bad news that her mother was badly injured in the accident.
A. must know
B. might have known
C. must have known
D. should have known
答案：
A. must know
B. might have known
(答案→)C. must have known
D. should have known
解析：考查虚拟语气.句意:玛丽哭得很伤心._哦,她一定是知道了她的母亲在车祸中严重受伤的坏消息了. “must+have+done”表示对过去事情的肯定推测，译成“一定做过某事”，该结构只用于肯定句。结合语境可知选C.
