什么时候用完成时

什么时候用完成时
①表示动作发生在过去某个不确定的时间，但对现在留下了某种影响和结果。

常被just、already、yet等副词修饰。

如：
-Have you had lunch yet? -Y es, I have. I've just had it.
你（已经）吃午饭了吗？我刚刚吃过。

（现在我不饿了）
②表示从过去某一时刻开始一直持续到现在的动作或状态。

这个动作可能刚停止，可能仍然在进行。

常带有for和since等表示一段时间的状语。

如：He has taught here since 1981
他自1981年就在这儿教书。

（可能还要继续教）
I haven’t seen her for four years.
3 现在完成时用法总结
⑴与时间状语so far, till now, up to now, for + 一段时间, before, ever, never, recently, just, already, yet 等时间状语的句子中, 谓语常用现在完成时.
I have planted fourteen trees so far.
Have you ever been to Europe before?
I have learned English for three years.
She has not yet studied French well.
⑵用在特定句型中
ⅰThis /It is the first /second…/last time (that) …” that常省略, 表示“这是某人第几次做某事” 常常用完成时态. 如果主句用一般现在时, 从句用现在完成时。

主句用一般过去时, 从句用过去完成时。

It is the third time that I have seen the film.
It is my first time that I have been to Shanghai.
It was the first time I had seen a fantasy film.
ⅱIt is / has been… since…句型中, 主句常用现在完成时,但since从句用一般过去时.
It has been three years since she graduated from Beijing University.
自她北大毕业以来已经三年了.
ⅲThis is one of the most attractive places I’ve been to. 被形容词最高级所修饰的名词后的定语从句中，一般用完成时态。

This is the most delic ious food I’ve ever eaten. 这是我所吃过的最美味的食物。

She is the most beautiful girl I’ve seen.
她是我见过的最美丽的姑娘
⑶与时间状语in the past 连用时, 谓语常用过去时, 而与in/over/during the past/last +数词+时间名词连用时常用现在完成时.
In the past three years, we have stayed together all the time.
In the past century, soccer has become the most popular sport in the world.
现在完成时的句子中, 当出现表示“一段时间” 的状语时,如for three years, in the past three years, since 2005, 谓语只能是延续性动词.
She has worked in that factory for five years. He has lived in Shenzhen since 2002.。