现在完成时
1. 构成方法
have/has +动词的过去分词
现在完成时的否定式是在have/has的后面直接加not；
变为疑问句时，要将have/has提到主语之前。
2. 现在完成时态常与一些时间状语连用：
yet, already, just, before, ever, never, recently, so far, till/until, up to now, in the
a) since + 过去一个时间点（1980, March)
I have been here since 1989.
b) since + 一段时间+ ago
I have been here since five months ago.
c) since + 从句
Great change have taken place since you left.
d) It is + 一段时间+ since 从句（过去时）
It is twelve years since I became a student.
4. For 引导的表示一段时间的状语
They have been in Canada for ten years.
My brother has kept this book for 5 weeks. (特殊疑问句)
→How long has your brother kept this book?
5. 现在完成时与一般过去时的区别
一般过去时的时间状语：yesterday , last week, two days ago, in 2000, just now …
6. have gone to, have been to, have been in
a. Jim has gone to London with his family.
(He is on his way or in London now)
b. Jim has been to London before.
(He is back now.)
c. Jim has been in London for two weeks.
(He went to London two weeks ago and he is still there)
7. 延续性动词与终止性动词
终止性动词不可延续,所以不可与表示一段时间的状语连用.
误: I’ve left my hometown for 10 years.
正: I’ve been away from my hometown for 10 years.
误: He has borrowed this book for a week.
正: He has kept this book for a week.
但它们的否定式可以与一段时间状语连用.
Eg. I haven’t bought any new clothes for three months.
8. 终止性动词与表示一段时间的状语连用时, 将终止性动词转化为持续性动词come →be in… go →be in…
die →be dead borrow →keep
buy →have join →be in…/ be a …member
leave →be away
Eg. I came here for three years. (×)
→I have been here for three years.
The old man died for two months. (×)
→The old man has been dead for two months.
