Look! The light in the room is still on. Mr. Liu at work.A. mustB. can’t beC. must beD. ha

问题补充：

Look! The light in the room is still on. Mr. Liu at work.

A. must

B. can’t be

C. must be

D. have to be

答案：

A. must

B. can’t be

(答案→)C. must be

D. have to be

解析：

这题考查情态动词表示猜测的用法：can’t be一定不是must be一定是，根据句意：看房间的灯还开着，说明刘先生一定还在工作。选C。