(完整)现在完成时语法
现在完成时的基本句型:
肯定式:主语 + 助动词have/has + 动词的过去分词.
疑问式:助动词Have/Has + 主语 + 动词的过去分词?
否定式:  主语 + 助动词have/has + not + 动词的过去分词。
例句:
1.    I have cleaned my room。 我已打扫了房间。
2.    He hasn’t finished his homework。 他还没完成作业。     
3。    Have you read this novel ? 你看过这本小说吗?
    Yes , I have. 是的,看过了。No, I haven’t. 不,没看过。
4.    We have studied English for two years。
我们已经学了两年英语了.
5. They haven’t seen each other since 1998.
自从1998年他们就没再见过面.
现在完成时的主要用法
1.表示过去发生的某一动作对现在造成的影响或结果。
-— It's so dark。
-—Someone has turned off the light.
(有人刚把灯关了,对现在造成的结果是:现在很黑)
-—  Are you free?
-—I have finished my homework. I am free
(我已经完成了家庭作业,对现在造成的结果是很有空)
昨天已成过去
2.表示过去已经开始, 持续到现在的动作或状态,可以和表示从过去某一时刻延续到现在的一
段时间的状语连用。表示持续动作或状态的词应是延续性动词.常与since + 过去的时间点,since+谓语是一般过去时的从句;for + 一段时间,so far 等时间状语连用。如:
I have learnt English for more than ten years.我已经学了10多年的英语。
(从10年前开始,持续到现在还在学)
She has swum since half an hour ago。我已经游泳了半个小时
(半个小时前已经开始游泳,到现在还在游)
3。表示人曾有过或到目前为止从未有过的经历。
I have ever been to the Summer Palace?(我曾去过颐和园)
I have never had a car。(我从未有过汽车。)
现在完成时的时间状语
常与①already, ②never,  ③ever, ④just(刚才),  ⑤yet,  ⑥before, ⑦up to now,  ⑧so
far(到目前为止), ⑨for the last few weeks, ⑩these days, ⑾since 2010/ two years ago, since he came here, ⑿for a long time (13) in the last/ past…years等连用.
a)already 往往用于肯定句,用在疑问句时表示强调或加强语气;yet 用于否定句和疑问句.eg:
He has already left here. 他已经离开这里了。
Has he already left here?
他(真的)已经离开这里了吗?(表示加强语气)
My teachers haven’t had breakfast yet. 我的老师们还没有吃早饭。
Have you written to your parents yet? 你已经给你父母写过信了吗?
b) never 是否定词,表示“从来没有",而ever 表示“曾经"
We have never been to the Great Wall. 我们从来没有去过长城.
Have you ever been to Canada?    你们曾经去过加拿大吗?
c) just表示“刚刚”(用于完成时态时,与already,never 等副词的位置一样,多用在助动词have/has和动词过去分词之间),just now(用于过去时)
He has just come back.  他刚刚回来。
They have just finished the work. 他们刚刚完成那项工作.
d) before 用于完成时,而ago 用于过去时
He has started his work ten years before。 
他十年前就已经开始他的工作了。
He started his work ten years ago. 他是十年前开始他的工作的。
常用于现在完成时的时间副词,介词:
already (已经): 用于肯定句I have already posted the letter 。
yet(已经): 用于否定句,疑问句 He hasn't done his homework yet.
just(刚刚) They have just left.
ever(曾经) Have you ever been to Beijing ?
never(从不) I have never seen him .
before(以前) Have you seen the film before?
since(自从…以来) I’ve worked in the school since 1999.
for(长达) He's lived in Shenzhen for 6 years.
in the past several days / weeks/ years(在过去的…)
recently(最近) I have not written to my parents recently。
so far(到目前为止)  So far she has learned 5 English songs.
up to now(到目前为止)
this morning/month/year(今天早上/这个月/今年)
现在完成时与一般过去时的区别
I lived there 2 years ago
I have lived here for two years
I have lived here since two years ago.
I have lived here since I came here.
1。都表示过去发生的事
2.现在完成时强调过去和现在的联系,不能和具体的时间状语连用;
3。一般过去时强调过去发生的事或状态与表示过去的具体时间连用(last, ago, yesterday, etc。 )
当有一个表示过去某时的状语时,不能用现在完成时,而多用一般过去时。
    I saw Mary an hour ago.
      She lost her handbag yesterday .
有些时间状语,既能用于现在完成时,又能用于一般过去时,但意义上有差别。
I've written three letters this morning。(说话时仍是上午)
I wrote three letters this morning.(说话时仍是上午或晚上)
现在完成时强调动作或事情发生在过去,一直延续到现在,而且还有可能继续延续下去;而一般过去时只表示发生在过去的动作或事情。
  I have taught this class for ten years.(还在教)
I taught this class for two years.(曾教过两年,现在不教了)
一般过去时态和现在完成时态同义转换
1.我们买这本书三年了。
We have had the book for three years.
We bought the book three years ago. 
2.他感冒三天了.
He has had a cold for three days
He caught a cold three days ago.
3。我借的这本书一周多了.
I have kept the book for a week .

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