It's two years since I worked in Beijing.为什么不能用has worked?He worked in Africa on wild animals fo

题目

It's two years since I worked in Beijing.为什么不能用has worked?

He worked in Africa on wild animals for eight years.为什么不能用had worked?

Our work not finished ,we refused his offer.为什么不能用has not been finished?

答案

你的第一句最好加上last,这样你就明白了：
It's two years since I LAST worked in Beijing.---------不在那里工作已经两年了.
第二句只强调在过去,到底是怎样的过去无所谓,与“今天“没有任何关系,所以只用”一般过去时“.如果是had worked,句子应该是这样的：
He had worked in Africa on wild animals for eight years before he came to be our biology teacher last year.--------过去的过去,用”过去完成时“.
Our work not finished == as our work hadn't been finished yet -------你的是独立主格结构,我的是原因状语从句结构.-------独立主格结构需要去掉助动词had 和been,保留真正动词.