Unit 6 How long have you been collecting shells?
语法 现在完成时 （have/has+过去分词）
一、 基本构成
1． 肯定句：
主语（第一、二人称，第三人称复数）+have +过去分词+其他
主语（第三人称单数）+has+过去分词+其他
2． 否定句 主语+ have/has +not +过去分词+其他
3． 一般疑问句 Have/Has +主语+过去分词+其他？
4． 特殊疑问句 特殊疑问词+have/has +主语+过去分词+其他？
二、 现在完成时的用法
1．表示过去发生或已经发生的某一动作对现在造成的结果或影响，可以和already ,yet, just连用。
(1) I have already posted the photos .我已经把照片寄了。（照片已不在我这儿了）
(2) Have you had your lunch yet? 你已经吃午饭了？
Yes, I have . I’ve just had it .是的， 我吃了。 我刚刚吃的。（现在不饿了）
2． 表示过去已经开始，持续到现在还可能继续下去的动作或状态，可以和表示过去的某一时刻延续到现在（包括“现在”在内）的一段时间的状语连用。如：these days, by the end of …,（到。。。为止） since (自从。。。以来) ， for+一段时间， so far (到目前为止)
（1） She’s been there for over two years 她在那两年多了。
（2） They’ve lived here since 1989.
注意：问句时常用How long …..? 提问现在完成时的时间。
3．表示从过去到现在之间曾经历过的事情，常和never ,once , three times , before等连用。
（1）I have never been to Egypt before .以前我从没去过埃及。
（2）She has gone to France .她去法国了。
（她可能在去法国的路上或已经到法国，人没有回来，总之不在这里了）
三、 现在完成时与一般过去时的区别
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；
现在完成时为过去发生的，强调过去的事情对现在的影响，强调的是影响。
2）过去时常与具体的时间状语连用，而现在完成时通常与模糊的时间状语连用，或无时间状语。
一般过去时的时间状语:
yesterday, last week，…ago, in1980, in October, just now, 具体的时间状语
共同的时间状语:
this morning, tonight,this April, now, once，before, already, recently，lately
现在完成时的时间状语
for, since, so far, ever, never, just, yet, till / until, up to now, in past years, always,
不确定的时间状语
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。
举例：
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。）
Why did you get up so early?（强调起床的动作已发生过了。）
Who hasn't handed in his paper? （强调有卷子，可能为不公平竞争。）
She has returned from Paris. 她已从巴黎回来了。
She returned yesterday. 她是昨天回来了。
He has been in the League for three years.(在团内的状态可延续)
He has been a League member for three years.(是团员的状态可持续)
He joined the League three years ago. ( 三年前入团，joined为短暂行为。)
I have finished my homework now.
---Will somebody go and get Dr. White?
---He's already been sent for.
注意：句子中如有过去时的时间副词（如 yesterday, last, week, in 1960）时，不能使用现在完成时，要用过去时。
（错）Tom has written a letter to his parents last night.
（对）Tom wrote a letter to his parents last night.
四、用于现在完成时的句型
1． It is the first / second time…that…结构中的从句部分，用现在完成时。
It is the first time that I have visited the city.
It was the third time that the boy had been late.
2． This is the… that…结构，that 从句要用现在完成时.
This is the best film that I've (ever) seen. 这是我看过的最好的电影。
This is the first time (that) I've heard him sing.这是我第一次听他唱歌。
典型例题
(1) ---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
答案B. This is the first time 后面所加从句应为现在完成时，故选B。
(2) ---Have you ____ been to our town before?
---No, it's the first time I ___ here.
A. even, come B. even, have come C. ever, come D. ever, have come
答案D. ever意为曾经或无论何时，反意词为never，此两词常用于完成时。 This is the largest fish I have ever seen. It is / was the first time +that-clause 的句型中，从句要用完成时
五、 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.
Some new oilfields have been opened up since 1976.
I have known Xiao Li since she was a little girl.
My brother has been in the Youth League for two years.
I have not heard from my uncle for a long time.
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。)
小窍门：当现在完成时+一段时间，这一结构中，我们用下面的公式转化，很容易就能排除非延续动词在完成时中的误使。
1)(对) Tom has studied Russian for three years.
= Tom began to study Russian three years ago, and is still studying it now.
2)(错) Harry has got married for six years.
= Harry began to get married six years ago, and is still getting married now.
显然，第二句不对，它应改为 Harry got married six years ago.或 Harry has been married for six years.
六、 瞬间动词和持续动词瞬间动词的转换
瞬间动词
持续动词
瞬间动词
瞬间动词
Leave
Close
Buy
Catch a cold
borrow
fall ill
die
fall asleep
get up
come back
put on(上演)
Be away from
Be not open
have
have a cold
keep
be ill
dead
be sleeping
be up
be back
be on
Open
Join the party
Join the club
Join the army
work
study
Begin to learn
teach
Be open
Be a pary member
be in the party
be a member /be in the club
be a soldier/be in the army.
work
stuy
去掉begin to