He is an hour late by now．He last night．
A. must stay up
B. should stay up
C. should have stayed up
D. must have stayed up
网友回答
A. must stay up
B. should 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。根据last night，可知是指过去的事情，要用情态动词加完成时态，表对过去事实的推测，排除A,B；should have stayed up本应该熬夜而实际没有，must have stayed up表肯定熬夜了。根据他迟到这一事实，可知他昨晚肯定熬夜了，才导致迟到这一事实，所以选D。