三、谓语动词提前一个时态（在原来时态的基础上再”过去”一下）
1.wish后的宾语从句，e.g.:
I wish I had been to the concert last night.
I would (had) rather后的句子
I’d rather he hadn’t done anything like that.

五、由as if，as though引导的从句中，表示对现在的怀疑：用一般过去时
对过去的怀疑：用过去完成时 e.g.:
She looks as if she knew all about it.
if only引导的感叹句中，表示与现在相反：用一般过去时
表示与过去相反：用过去完成时 e.g.:
If only he knew our telephone number!