现在完成时转换成一般过去时
现在完成时转换成一般过去时
作者: admin来源: 网络文章 时间: 2016-07-23
现在完成时可以转化成一般过去时，还可以转化成“It is/has been +时间段+since从句(用一般过去时)”等句型。
e.g. Jim has been back for a month. 吉姆已经回来一个月了。 = Jim came back a month ago. 吉姆一个月前就回来了
= It is/has been a month since Jim came back. 自吉姆回来已经有一个月了。 = A month has passed since Jim came back. I have kept the book for two days. = I borrowed the book two days ago.
= It is / has been two days since I borrowed the book. = Two days has passed since I borrowed the book.
比较过去时与现在完成时
作者: admin来源: 网络文章 时间: 2013-02-27
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.
比较since和for
作者: admin来源: 网络文章 时间: 2013-02-27
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.
昨天已成过去
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.

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