现在完成时用来表示之前已发生或完成的动作或状 态，其结果的确和现在有联系。动作或状态发生在过去 但它的影响现在还存在；也可表示持续到现在的动作或 状态。其构成： have (has) +过去分词。
一般过去时的用法
1）在确定的过去时间里所发生的动作或存在的状态。
时间状语有：yesterday, last week, an hour ago, the other day, in 1982等。
Where did you go just now?
2）表示在过去一段时间内，经常性或习惯性的动作。
When I was a child, I often played football in the street.
Whenever the Browns went during their visit, they were given a warm welcome.
3）句型：
It is time for sb. to do sth "到……时间了" "该……了"
It is time sb. did sth. "时间已迟了" "早该……了"
It is time for you to go to bed. 你该睡觉了。
It is time you went to bed. 你早该睡觉了。
would (had) rather sb. did sth. 表示'宁愿某人做某事'
I'd rather you came tomorrow.
4) wish, wonder, think, hope 等用过去时，作试探性的询问、请求、建议等。
I thought you might have some. 我以为你想要一些。
比较：
一般过去时表示的动作或状态都已成为过去，现已不复存在。
Christine was an invalid all her life.
(含义：她已不在人间。)
Christine has been an invalid all her life.
(含义：她现在还活着)
Mrs. Darby lived in Kentucky for seven years.
(含义：达比太太已不再住在肯塔基州。)
Mrs. Darby has lived in Kentucky for seven years.
( 含义：现在还住在肯塔基州，有可能指刚离去)
注意： 用过去时表示现在，表示委婉语气。
1）动词want, hope, wonder, think, intend 等。
Did you want anything else?
I wondered if you could help me.
2）情态动词 could, would.
Could you lend me your bike?
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.
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.
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