—Peter looked tired and a little absent-minded in class．
—He too late．
A. may stay up
B. could stay up
C. should have stayed up
D. must have stayed up
网友回答
A. may stay up
B. could stay up
C. should have stayed up
(答案→)D. must have stayed up
解析：考查情态动词表推测的用法。must have done 表示对过去事情肯定的推测，句意： 皮特看起来很累在课上有点心不在焉。他一定熬夜熬得太晚了。所以选D。