11.12 比較since和for

　　Since 用來(lái)說(shuō)明動(dòng)作起始時(shí)間，for用來(lái)說(shuō)明動(dòng)作延續(xù)時(shí)間長(zhǎng)度。例如：

　　I have lived here for more than twenty years.我住在這兒二十多年了。

　　I have lived here since I was born. 我從出生起就住在這兒了。

　　注意：并非有for 作為時(shí)間狀語(yǔ)的句子都用現(xiàn)在完成時(shí)。

　　I worked here for more than twenty years. （我現(xiàn)在已不在這里工作。）

　　I have worked here for many years.（現(xiàn)在我仍在這里工作。）

　　注意：用句型轉(zhuǎn)換的方法，很容易排除非延續(xù)動(dòng)詞在有for/since結(jié)構(gòu)的完成時(shí)中的誤用。

　　1）（對(duì)） Tom has studied Russian for three years. = Tom began to study Russian three years ago, and is still studying it now.

　　2）（錯(cuò)） Harry has got married for six years. = Harry began to get married six years ago, and is still getting married now.

　　顯然，第二句不對(duì)，它應(yīng)改為 Harry got married six years ago. 或 Harry has been married for six years.

　　11.13 since的四種用法

　　1） since +過(guò)去一個(gè)時(shí)間點(diǎn)（如具體的年、月、日期、鐘點(diǎn)、1980, last month, half past six）。例如：

　　I have been here since 1989. 1989起，我一直在這兒。

　　2） since +一段時(shí)間+ ago。例如：

　　I have been here since five months ago. 我在這兒，已經(jīng)有五個(gè)月了。

　　3） since +從句。例如：

　　Great changes have taken place since you left. 你走后，變化可大了。

　　Great changes have taken place since we were here. 我們走后，變化可大了。

　　4） It is +一段時(shí)間+ since從句。例如：

　　It is two years since I became a postgraduate student. 我考上研究生有兩年了。

　　11.14 延續(xù)動(dòng)詞與瞬間動(dòng)詞

　　1） 用于完成時(shí)的區(qū)別

　　延續(xù)動(dòng)詞表示經(jīng)驗(yàn)、經(jīng)歷； 瞬間動(dòng)詞表示行為的結(jié)果，不能與表示段的時(shí)間狀語(yǔ)連用。例如：

　　He has completed the work.　　他已完成了那項(xiàng)工作。 （表結(jié)果）

　　I've known him since then.　　 我從那時(shí)起就認(rèn)識(shí)他了。（表經(jīng)歷）

　　2） 用于till / until從句的差異

　　延續(xù)動(dòng)詞用于肯定句，表示"做……直到……" 瞬間動(dòng)詞用于否定句，表示"到……，才……"。例如：

　　He didn't come back until ten o'clock. 他到10 點(diǎn)才回來(lái)。

　　He slept until ten o'clock.　 他一直睡到10點(diǎn)。

　　典型例題

　　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. 首先本題后句強(qiáng)調(diào)對(duì)現(xiàn)在的影響，我知道她的模樣，你不用描述。再次，several times告知為反復(fù)發(fā)生的動(dòng)作，因此用現(xiàn)在完成時(shí)。

　　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. 等待的動(dòng)作由過(guò)去開(kāi)始，持續(xù)到現(xiàn)在，應(yīng)用現(xiàn)在完成時(shí)。

　　11.15 過(guò)去完成時(shí)

　　1） 概念：表示過(guò)去的過(guò)去

　　----|----------|--------|----> 其構(gòu)成是had +過(guò)去分詞構(gòu)成。

　　那時(shí)以前　 那時(shí)　現(xiàn)在

　　2） 用法

　　a. 在told, said, knew, heard, thought等動(dòng)詞后的賓語(yǔ)從句。例如：

　　She said （that）she had never been to Paris. 她告訴我她曾去過(guò)巴黎。

　　b. 狀語(yǔ)從句

　　在過(guò)去不同時(shí)間發(fā)生的兩個(gè)動(dòng)作中，發(fā)生在先，用過(guò)去完成時(shí)；發(fā)生在后，用一般過(guò)去時(shí)。例如：

　　When the police arrived, the thieves had run away. 警察到達(dá)時(shí)，小偷們?cè)缇团芰恕?/p>

　　c. 表示意向的動(dòng)詞，如hope, wish, expect, think, intend, mean, suppose等，用過(guò)去完成時(shí)表示"原本…，未能…"。例如：

　　We had hoped that you would come, but you didn't. 那時(shí)我們希望你能來(lái)，但是你沒(méi)有來(lái)。

　　3）　過(guò)去完成時(shí)的時(shí)間狀語(yǔ)before, by, until , when, after, once, as soon as。例如：

　　He said that he had learned some English before. 他說(shuō)過(guò)他以前學(xué)過(guò)一些英語(yǔ)。

　　By the time he was twelve, Edison had began to make a living by himself. 到了十二歲那年，愛(ài)迪生開(kāi)始自己謀生。