1．构成：have / has + 过去分词
2．功能：
（1）表示过去所发生的动作对现在的影响或产生的结果。常与yet, just, before, recently, lately（最近）, ever, never等表时间的副词搭配使用。
He hasn't seen her lately.
I haven't finished the book yet.
（2）表示一个从过去某个时间开始，延续到现在并可能持续下去的动作，常与表示一段时间的时间状语连用。如：so far（迄今为止）, up till now（直到现在）, since, for a long time（很长时间）, up to present（直到现在）, in the past / in the last few years（在过去的几年里）, these days（目前）……
He has worked here for 15 years.
I have studied English since I came here.
The foreigner has been away from China for a long time.
So far, I haven't received a single letter from my brother.
（3）某些非延续性动词（即：动作开始便终止的动词），在现在完成时中不能与表示一段时间状语搭配。
黄金要点：
I．常见的非延续动词：die, arrive（到达）, join（加入）, leave（离开）, go, refuse（拒 绝）, fail（失败）, finish, buy, marry, divorce（离婚）, awake（醒）, buy, borrow, lend ... （背三遍！）
II．这类动词并非不能用现在完成时，而是不能接常由for引导的时间状语。
III．但若是用在否定句中，非延续动词的现在完成时可以与表示一段时间的状语连用。
She has gone away for a month.（误）
She has been away for a month （正）
The man has died for two years.（误）
The man has been dead for two years.（正）
How long have youbought the book?（误）
How long have you got the book.（正）
（4）注意 since的用法：
They haven't had any trouble since they came here.
It has been ten years since we met last time.
He has been here since 1980.
He has been here since ten years ago.
几组对比：
He has gone to Shanghai. 他到上海去了。
He has been to Shanghai. 他去过上海。
She has gone. 她已走了。
She is gone. 她缺席了。（或者她死了。）
The door has been closed. 门关上了。（动作）
The door is closed. 门是关着的。（状态）
