现在完成时：其构成： have (has) +done
用法：
1）表示过去发生的动作对现在的影响或结果；
I’ve seen the film Avatar before.
2）表示持续到现在的动作或状态。
They’ve lived there for eleven years.
比较过去时与现在完成时
1）过去时表示过去某时发生的动作或单纯叙述过去的事情，强调动作；现在完成时强调过去的事情对现在的影响，强调的是影响。
I saw this film yesterday.（强调看的动作发生过了。）
I have seen this film. （强调对现在的影响，电影的内容已经知道了。）
2）过去时常与具体的时间状语yesterday, last week，…ago, in1980, in October, just now等连用，而现在完成时通常与模糊的时间状语for, since, so far, ever, never, just, before, yet, till / until, up to now, in past years, always等连用，或无时间状语。
共同的时间状语:
this morning, tonight, this April, now, once，before, already, recently，lately
3）现在完成时可表示持续到现在的动作或状态，动词一般是延续性的，如live, teach, learn, work, study, know.
过去时常用的非持续性动词有come, go, leave, start, die, finish, become, get married等。
用于现在完成时的句型
1）It is the first / second time…. that…
It is the first time that I have visited the city.
2）This is the… that…
This is the best film that I''ve (ever) seen.
注意：非延续性动词的否定形式可以与表示延续时间的状语连用。即动作不发生的状态是可以持续的。
I haven''t received his letter for almost a month.
比较since和for
since 用来说明动作起始时间，for用来说明动作延续时间长度。
I have lived here for more than twenty years.
I have lived here since I was born..
My aunt has worked in a clinic since 1949.
注意：并非有for 作为时间状语的句子都用现在完成时。
I worked here for more than twenty years. (我现在已不在这里工作。)
I have worked here for many years.(现在我仍在这里工作。)
延续动词与瞬间动词
1) 用于完成时的区别
延续动词表示经验、经历； 瞬间动词表示行为的结果，不能与表示段的时间状语连用。
He has completed the work. (表结果)
I''ve known him since then. (表经历)
2)用于till / until从句的差异
延续动词用于肯定句，表示"做……直到……"； 瞬间动词用于否定句，表示"到……，才……"
He didn''t come back until ten o''clock.
He slept until ten o''clock.
1.把考察放在从句中增加难度；2.和被动语态放在一起考察；3.根据状语确定时态4.用现在完成时的句型
1.现在完成和一般过去弄混；2.现在完成时的句型不熟悉；3. 不能根据状语选定现在完成时。
【典型例题】
1. You don''t need to describe her. I ___ her several times.
A. had met B. have met C. met D. meet
解析：错选C。首先本题后句强调对现在的影响，我知道她的模样，你不用描述；再次，“several times” 表示“（到目前为止）我（已经）见过她 “好几次”了，因此用现在完成时，答案B。
2. ---I''m sorry to keep you waiting.
---Oh, not at all. I ___ here only a few minutes.
A. have been B. had been C. was D. will be
解析：错选C。等待的动作由过去开始，持续到现在，应用现在完成时，答案A。
3. ---Do you know our town at all?
---No, this is the first time I ___ here.
A. was B. have been C. came D. am coming
解析：错选D。This is the first time 后面所加从句应为现在完成时，答案B。
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