- Excuse me may I keep the book a little longer? - Sorry. You return it today.A. mustB.

问题补充：

- Excuse me, may I keep the book a little longer? - Sorry. You return it today.

A. must

B. mustn

C. can

D. can

答案：

(答案→)A. must

B. mustn

C. can

D. can

解析：句意：—对不起，请问这本书我可以多看一段时间吗？—很抱歉。今天你必须还。A. must必须；B. mustn 禁止；C. can能、会；D. can 不能。句意和词意结合可知，选A。