He is an hour late by now．He last night．
A. must stay up
B. should stay up
C. must have stayed up
D. should have stayed up
网友回答
A. must stay up
B. should stay up
(答案→)C. must have stayed up
D. should have stayed up
解析：考查虚拟语气。句意：到现在他已经迟了一个小时。他昨晚肯定熬夜了。“must+have+done”表示对过去事情的肯定推测，译成“一定做过某事”。故选C。