— Hi Mary. Any idea where Bill is?— He in the library. I saw him reading books there jus

问题补充：

— Hi, Mary. Any idea where Bill is?

— He in the library. I saw him reading books there just now.

A. shall be

B. should have been

C. must be

D. might have been

答案：

A. shall be

B. should have been

(答案→)C. must be

D. might have been

解析：虚拟语气辨析。句意：嗨，玛丽，知道比尔在哪儿吗？——他一定在图书馆。我刚才看到她在那儿读书了。可知下文是对事实的肯定判断，不用虚拟语气，故选C。