--Why are your eyes so red? You have slept well last night.
A. can't
B. mustn't
C. needn't
D. won't
网友回答
(答案→)A. can't
B. mustn't
C. needn't
D. won't
解析：考查情态动词：句意：你眼睛怎么这么红？你昨晚一定没睡好吧。---我熬夜写报告。根据why are your eyes so red？可以得出对方一定没有睡好，故用can’t（不可能）。Mustn’t（禁止，不准）；needn’t（不必）；won’t（不会）。选A。