关于完成与过去时态的问题

题目

关于完成与过去时态的问题
句子：(1)I didn't realize what disaster I had brought to you until I had checked out what had heppened.(2)I have been working in Shenzhen for four years since I gruduated from university.
我的疑问：1,在第（1）句中,until后为什么用的的是过去完成时I had checked out而不是过去时I checked out?2,在第（2）句中,since后为什么用的不是过去完成时I had grduated而是I graduated呢?其实我就是不懂过去时与过去完成时的用法,常常搞混.

答案

小分析一下：
首先看第一个句子：I didn't realize what disaster I had brought to you until I had checked out what had heppened.
didn't realize 已经是过去时,而check out是在didn't realize 之前的动作,属于过去的过去,故而用过去完成时.
再来看第二个句子：I have been working in Shenzhen for four years since I gruduated from university.
since后面接的是一个时间点,在那个时间点,是过去时的时间状语,你毕业,所以应该是过去时.如果要用过去完成时,你不妨问问自己,那个在毕业之前发生的动作在哪呢?显然找不到……这个句子相当经典,建议您背下来以免犯同样错误.
过去完成时,是指过去的过去,而过去时,指过去,而不含有过去的过去的意思.
希望对您有帮助.