(2013•四川，5)—why are your eyes so red？you________have slept well last night. —yeah，i stayed up late writing a report. a．can't b．mustn't c．needn't d．won't 解析 考查情态动词。根据语境“眼睛那么红，昨晚不可能睡得很好”可知，此处考查情态动词can的否定式can't表推测，意为“不可能”。can't have done表示对过去的推测，意为“过去不可能……”。故选a。答案 a
