since的四种用法
1） since +过去一个时间点（如具体的年、月、日期、钟点、1980, last month, half past
six）。例如：
- I have been here since 1989. 1989起，我一直在这儿。
2） since +一段时间+ ago。例如：
- I have been here since five months ago. 我在这儿，已经有五个月了。
3） since +从句。例如：
- Great changes have taken place since you left. 你走后，变化可大了。
- Great changes have taken place since we were here. 我们走后，变化可大了。
4） It is +一段时间+ since从句。例如：
It is two years since I became a postgraduate student. 我考上研究生有两年了。
延续动词与瞬间动词
1） 用于完成时的区别
延续动词表示经验、经历； 瞬间动词表示行为的结果，不能与表示段的时间状语连用。例如：
He has completed the work. 他已完成了那项工作。 （表结果）
I've known him since then. 我从那时起就认识他了。（表经历）
2） 用于till / until从句的差异
延续动词用于肯定句，表示"做……直到……" 瞬间动词用于否定句，表示"到……，才……"。例如：
He didn't come back until ten o'clock. 他到10 点才回来。
He slept until ten o'clock. 他一直睡到10点。
典型例题
1. You don't need to describe her. I ___ her several times.
A. had met B. have met C. met D. meet
答案B. 首先本题后句强调对现在的影响，我知道她的模样，你不用描述。再次，several times告知为反复发生的动作，因此用现在完成时。
2. ---I'm sorry to keep you waiting.
---Oh, not at all. I ___ here only a few minutes.
A. have been B. had been C. was D. will be
答案A. 等待的动作由过去开始，持续到现在，应用现在完成时。
过去将来时
指对过去的某一个时间来讲，将要发生的动作。
动词由would+动词原型构成。
例句
He would go to the park the next day.
He said he would work hard next term.
过去完成时
指对过去的某一个时间来讲，已经发生的动作。
动词由had+过去分词构成。
例句
she had borrowed a book before she went to the park.
We had learned many new words by the end of last term.
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。例如：
She said （that）she had never been to Paris. 她告诉我她曾去过巴黎。
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。例如：
When the police arrived, the thieves had run away.
警察到达时，小偷们早就跑了。
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…"。例如：
We had hoped that you would come, but you didn't.
那时我们希望你能来，但是你没有来。
3） 过去完成时的时间状语before, by, until , when, after,once, as soon as。例如：
He said that he had learned some English before. 他说过他以前学过一些英语。
By the time he was twelve, Edison had began to make a living by himself. 到了十二岁那年，爱迪生开始自己谋生。
Tom was disappointed that most of the guests had left when he
arrived at the party.
汤姆失望了，因为他到达晚会时，大部分客人已经走了。
典型例题
The students ___ busily when Miss Brownwent 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。
注意： had hardly… when 还没等…… 就……。例如：
I had hardly opened the door when I he hit me. 我刚打开门，他就打了我。had no sooner…than 刚…… 就……。例如：
He had no sooner bought the car than he sold it.
他刚买了这辆车，转眼又卖了。
用一般过去时代替过去完成时
1） 两个动作如按顺序发生，又不强调先后，或用then，and，but 等连词时，多用一般过去时。例如：
When she saw the mouse，she screamed. 她看到老鼠，就叫了起来。
My aunt gave me a hat and I lost it. 姑妈给了我一顶帽子，我把它丢了。
2 ） 两个动作相继发生，可用一般过去时；如第一个动作需要若干时间完成，用过去完成时。例如：
When I heard the news, I was very excited.
3） 叙述历史事实，可不用过去完成时，而只用一般过去时。例如：
Our teacher told us that Columbus discovered America in 1492.
将来完成时
1） 构成will have done
2） 概念
a. 状态完成：表示某事继续到将来某一时为止一直有的状态。例如：
They will have been married for 20 years by then.
到那时他们结婚将有二十年了。
b. 动作完成：表示将来某一时或另一个将来的动作之前，已经完成的动作或获得的经验。例如：
You will have reached Shanghai by this time tomorrow.
明天此时，你已经到达上海了。
语态有两种：
主动语态和被动语态
|
