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【知识总结归纳】
一、现在完成时的时间状语
现在完成时的时间状语（包括副词、短语、从句等）主要有三种类型，分别用于不同意义的句子之中。
1. 表达“现在刚刚完成”的动作：
副词：just, already, yet, recently（lately）, etc.
短语：so far, these+（最近）一段时间，etc.
2. 表达某种经历或经验
副词：ever, never, once, twice, before, etc.
常用句：How many times…?
3. 表达“过去继续到现在的动作或状态”，常与for和since连用。如：
for two weeks, for a long time since+过去时间点/n./一段时间+ago/一般过去时的从句
在以上的时间状语中需要认真区别的就是“since+一段时间+ago”这个结构，它与“一段时间+ago”含义不同，前者为时间段，后者为时间点。
二、一般过去时与现在完成时的比较
1. 在表达“过去的经历、经验”的概念时，如果时间不确定，用现在完成时，如果时间确定，则用一般过去时。如：
I’ve met him before.
I met him two days ago.
2. 在when或what time引导的特殊疑问句中，不能用现在完成时。如：
When have you visited New York?
When did you visit New York?
3. 过去发生的连串动作，如用and, but, or, so等对等连词连接，要用一般过去时。
三、延续性动词与瞬间动词
例1： Mr. Green ____ for two hours.
A. has gone B. has left
C. has arrived D. has been away
例2： I ____ for six months.
A. have received John’s letter
B. have heard from John
C. haven’t heard from John
D. haven’t heard from John’s letter
以上两题都涉及了延续性动词与非延续性动词，即瞬间动词，所谓延续性动词，又称为持续性动词，即可以表示持久动作或状态的动词，如drink, eat, read, play, fly, talk等词，这些动词有以下特点：
（1）可以和表示时间段的状语连用
The students have played for an hour.
Mr. Green has read for about four hours.
He will stay there for two weeks.
（2）可以用于进行时态
I am writing an important letter.
It was raining hard when we got off the train.
瞬间动词，也叫终止性动词，暂时性动词或“点动词”，如open/close, leave, come, go, put, arrive, finish, borrow, lend, marry等动作在极短的瞬间时间内完成的，也就是说该动作一发生即直接转入结束，结果状态，这类词有以下特点：
（1）不能和表示一段时间的时间状语连用，试看以下例句：
① 我感冒一个星期了。
② 五天来我一直穿着那些蓝上衣。
（2）瞬间动词的否定形式可以表示状态，也就可以和“时间段”的状语连用。如：
I’ve not heard from him for a month.
I didn’t go to bed until 12 o’clock.
（3）瞬间动词用于进行时态时，一般指重复动作，而不是指一次动作，如：
He was jumping to keep warm.
He was knocking at the door.
延续性动词与瞬间动词可以在不同的句子结构或不同时态的句子之间进行相互转换，表达相同的意思。如：电影已经放映十分钟了。
The film began ten mimutes ago.The film has been on for ten minutes.
这两种动词的相互转换有三种形式：
1. 将瞬间动词转换成为延续性动词，并与表示时间段的状语连用。
He bought the book two weeks ago. He has had the book for two weeks.
His brother has been in the army for 3 months. His brother joined the army 3 months.
常用的这类转换有lend/borrow→keep buy→have，join→be in，marry→be married，open/close→be open/closed， die→be dead等。试完成这个句子转换：
John borrowed the book three days ago.
John ____ the book ____ three days.
2. 用“It is+时间段+since”句型进行转换。如：
He has studied in our school for four years.
It is four years since he came to study in our school.
在这类转换中，since所引导的从句为一般过去时，且谓语动词多为瞬间动词。试完成这个句子的转换：
Her mother died two years ago.
It is ____ since ____.
3. 用“时间段+has passed+since”句型进行转换，如：
I have been in the army for two years.
Two years has passed since I joined the army.
由此可见，刚才的句子“电影放映十分钟了”，还可以用上述的2、3句型来表达。即：
It is ten minutes since the film began.
和Ten minutes has passed since the film began.
一、现在完成时的时间状语
现在完成时的时间状语（包括副词、短语、从句等）主要有三种类型，分别用于不同意义的句子之中。
1. 表达“现在刚刚完成”的动作：
副词：just, already, yet, recently（lately）, etc.
短语：so far, these+（最近）一段时间，etc.
2. 表达某种经历或经验
副词：ever, never, once, twice, before, etc.
常用句：How many times…?
3. 表达“过去继续到现在的动作或状态”，常与for和since连用。如：
for two weeks, for a long time since+过去时间点/n./一段时间+ago/一般过去时的从句
在以上的时间状语中需要认真区别的就是“since+一段时间+ago”这个结构，它与“一段时间+ago”含义不同，前者为时间段，后者为时间点。
二、一般过去时与现在完成时的比较
1. 在表达“过去的经历、经验”的概念时，如果时间不确定，用现在完成时，如果时间确定，则用一般过去时。如：
I’ve met him before.
I met him two days ago.
2. 在when或what time引导的特殊疑问句中，不能用现在完成时。如：
When have you visited New York?
When did you visit New York?
3. 过去发生的连串动作，如用and, but, or, so等对等连词连接，要用一般过去时。
三、延续性动词与瞬间动词
例1： Mr. Green ____ for two hours.
A. has gone B. has left
C. has arrived D. has been away
例2： I ____ for six months.
A. have received John’s letter
B. have heard from John
C. haven’t heard from John
D. haven’t heard from John’s letter
以上两题都涉及了延续性动词与非延续性动词，即瞬间动词，所谓延续性动词，又称为持续性动词，即可以表示持久动作或状态的动词，如drink, eat, read, play, fly, talk等词，这些动词有以下特点：
（1）可以和表示时间段的状语连用
The students have played for an hour.
Mr. Green has read for about four hours.
He will stay there for two weeks.
（2）可以用于进行时态
I am writing an important letter.
It was raining hard when we got off the train.
瞬间动词，也叫终止性动词，暂时性动词或“点动词”，如open/close, leave, come, go, put, arrive, finish, borrow, lend, marry等动作在极短的瞬间时间内完成的，也就是说该动作一发生即直接转入结束，结果状态，这类词有以下特点：
（1）不能和表示一段时间的时间状语连用，试看以下例句：
① 我感冒一个星期了。
② 五天来我一直穿着那些蓝上衣。
（2）瞬间动词的否定形式可以表示状态，也就可以和“时间段”的状语连用。如：
I’ve not heard from him for a month.
I didn’t go to bed until 12 o’clock.
（3）瞬间动词用于进行时态时，一般指重复动作，而不是指一次动作，如：
He was jumping to keep warm.
He was knocking at the door.
延续性动词与瞬间动词可以在不同的句子结构或不同时态的句子之间进行相互转换，表达相同的意思。如：电影已经放映十分钟了。
The film began ten mimutes ago.The film has been on for ten minutes.
这两种动词的相互转换有三种形式：
1. 将瞬间动词转换成为延续性动词，并与表示时间段的状语连用。
He bought the book two weeks ago. He has had the book for two weeks.
His brother has been in the army for 3 months. His brother joined the army 3 months.
常用的这类转换有lend/borrow→keep buy→have，join→be in，marry→be married，open/close→be open/closed， die→be dead等。试完成这个句子转换：
John borrowed the book three days ago.
John ____ the book ____ three days.
2. 用“It is+时间段+since”句型进行转换。如：
He has studied in our school for four years.
It is four years since he came to study in our school.
在这类转换中，since所引导的从句为一般过去时，且谓语动词多为瞬间动词。试完成这个句子的转换：
Her mother died two years ago.
It is ____ since ____.
3. 用“时间段+has passed+since”句型进行转换，如：
I have been in the army for two years.
Two years has passed since I joined the army.
由此可见，刚才的句子“电影放映十分钟了”，还可以用上述的2、3句型来表达。即：
It is ten minutes since the film began.
和Ten minutes has passed since the film began.