问题
选择题
．If I _________too late last night, I could not have fallen asleep in class.
A．didn’t stay up
B．hadn’t stayed up
C．don’t stay up
D．haven’t stayed up
答案
答案：B
考查if条件状语从句的虚拟语气。If I _________too late last night是含有if条件状语从句的虚拟语气，根据last night可知是指的过去的事实，要用had done的过去完成时态，所以选B。