关于since引导时间状语从句时的用法
我们老师说若since引导的状语从句的谓语动词是持续性动词或表示状态的静态动词
(如live,stay,study,learn,smoke,be等)的过去时,
则从句表示的时间是“从该动作或状态的完成或结束时算起”.
如：
I’ve written her 20 letters since I have been here.
自从我来到这,我已经给她写了20封信.(从开始算起)
I’ve written her 20 letters since I was here.
自从我离开这儿,我已经给她写了20封信.(从结束算起)
但是课文有一句
That's changed since I was here.为什么要要理解成“我到这里之后一切就变了”?