主语用现在完成时,从句一般过去时
We've been friends ever since we left school.
我们在学校毕业后一直是朋友.
I've been engaged in this kind of work ever since I graduated from the university in 1990.
我自从1990年毕业以来就一直从事这项工作.
不懂追问*^__^* 主句要是过去时呢？可能么不可能