(1) 表示过去某一时刻发生，且延续到现在的动作或状态，这种情况常与表示一段的时间状语连用

We have lived here since last October. 自从去年十月份我们就一直住在这儿。

She has studied English for 5 years. 她学英语已有5年之久

(2) 表示某个已经发生且对现在造成影响或结果的动作，这种情况常不与任何时间状语连用

I'm sorry I have lost my key. I can't open the door.

对不起，我把钥匙弄丢了.门开不了了.

She has left. If you want to see her, you'll have to come tomorrow.

她已经走了.如果你想见她的话，你得明天再来一趟.