问题
选择题
I should not have laughed if I _________ you were serious.
A．thought
B．would think
C．had thought
D．have thought
答案
C
题目分析：句意：如果我认为你是严肃的，我不会笑的。根据should not have laughed可知这是对过去事实的假设，因此if引导的条件状语从句用过去完成时。故选C。
考点：