【题目】I should not have laughed if I ______ you were serious.
A.thought
B.would think
C.had thought
D.have thought

【答案】C
【解析】句意：如果我知道你是认真的话我就不笑了。本句意思是当时不知道所以笑了，表示与过去事实相反，用“had thought”表示对过去情况的虚拟 。故答案选“C”。