一、现在完成时
现在完成时分“完成用法”和“未完成用法”
1.现在完成时的"完成用法"
现在完成时的"完成用法"指的是动作发生在过去某一时刻并已结束,但该动作对现在产生了影响,与现在情况具有因果关系.例如：He has turned off the light.他已把灯关了.
(动作结束于过去,但说明的是现在的情况--灯现在不亮了.)
现在完成时"完成用法"的特点是动作不延续,因此,该时态只能与表示不定的过去时间状语(如：already,yet,before,recently等)、频度时间状语(如：never,ever,once等)、包括现在时刻在内的时间状语(如：this morning ／ month ／year...,today等)连用.
例如： Have you found your pen yet?你已找到你的钢笔了吗?
2.现在完成时的"未完成用法"
现在完成时的"未完成用法"指的是动作开始于过去某一时刻,一直延续到现在,或可能还要继续下去.
例如：He has lived here since 1978.自从1978年以来,他一直住在这儿.(动作起始于1978年,一直住到现在,可能还要继续住下去.)
此种用法的句中常需一个表示一段时间的状语(由since或for引导),或表示与现在时刻相连的时间状语(如：up to now,so far到目前为止)等.
例如：I have heard nothing from him up to now.到目前为止我没有他的任何消息.
注意：(1)现在完成时的未完成用法只适用于延续性动词,不可用于终止性动词,即瞬间完成或延续时间很短的动词.如：come,go,arrive,leave,join,become,die等.
(2)现在完成时常见两种句型：
①主语＋have / has been＋for短语
②It is＋一段时间＋ since从句
例如：He has been in the League for three years.或It is three years since he joined the League. 他入团已三年了.
二、过去将来时
过去将来时一般由或动词原形构成.第一人称用should或would+动词原形,第一人称用hould或would其余人称都用would.
2、过去将来时的一般用法：
过去将来一般时表示从过去某一时间来看将要发生或存在的状态,常用宾语从句中.e.g:Iwas sure that they wouldn't do that.过去将来时也可以用was(were)going to+动词原形was(were)+动词原形was(were)+动词的现在分词（多移动动词come go leave arrive来表示.e.g:No one knew when he was going to come./He said that they were to leave at six.
三、过去完成时
1） 概念：表示过去的过去
----|-------|-----|---->其构成是had +过去分词构成.
那时以前 那时 现在
2） 用法
a. 在told, said, knew, heard, thought等动词后的宾语从句.
She said (that) she had never been to Paris.
b. 状语从句
在过去不同时间发生的两个动作中,发生在先,用过去完成时；发生在后,用一般过去时.
When the police arrived, the thieves had run away.
c. 表示意向的动词,如hope, wish, expect, think, intend, mean, suppose等,用过去完成时表示"原本…,未能…"
We had hoped that you would come, but you didn't.
3) 过去完成时的时间状语before, by, until , when, after, once, as soon as.
He said that he had learned some English before.
By the time he was twelve, Edison had began to make a living by himself.
Tom was disappointed that most of the guests had left when he arrived at the party.
典型例题
The students ___ busily when Miss Brown went to get a book she ___ in the office.
A. had written, left B,were writing, has left C. had written, had left D. were writing, had left
答案D. "把书忘在办公室"发生在"去取书"这一过去的动作之前,因此"忘了书"这一动作发生在过去的过去,用过去完成时.句中when表示的是时间的一点,表示在"同学们正忙于……"这一背景下,when所引导的动作发生.因此
前一句应用过去进行时.
参考http://zhidao.baidu.com/question/227924485.html
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