“When”is used when the sentences refer to a single event in the past.“When”and“while”are used when the sentences refer to a period of time in the past.“As”is used when the sentences refer to a progressive change.Generally speaking,if the sentences refer to a single event in the past,either“when”,“while”or“as”will be OK.e.g.When/While/As I was walking down the street,I came across an old friend of mine.Besides,each of them has its own special usages.1)“when”can refer to either a single event in the past or a period in the past.e.g.When I lived there,I used to go to the seashore on Sundays.When the film ended,the people went back.As a young man(=when he was a young man),he was fond of hunting.2)“when”means“and at this/that time”,（表示（表示“这时，突这时，突然然.”）It is usually used in the following sentence patterns:Somebody was doing something when Somebody was about to/going to do something when Somebody was on the point of doing something when Somebody has just done something when e.g.We were having a meeting when someone break in.We were about to set off on our way,when it suddenly began to rain.3)“when”means“now that”.（含有“既然”的意思）It was foolish of you to take a taxi when you could easily walk there in five minutes.3)“when”means“now that”.（含有（含有“既然既然”的意思）的意思）e.g.It was foolish of you to take a taxi when you could easily walk there in five minutes.4)“while”clause refers to a period in the past.（含有（含有“在在期间期间”的意思）的意思）e.g.Please dont talk so loud while others are working.While I was wondering as this,our schoolmaster took his place.5)“while”expresses“contrast”.（表示（表示“而，却而，却”的意思）的意思）e.g.He likes pop music,while I am fond of folk music.6)“as”refers to a a progressive change.e.g.As the weather was getting cold,the leaves turned yellow and fell to the ground.7)“as”means“at the same time”.（表示（表示“一边一边一边一边”的意的意思）思）e.g.He hurried home,looking behind as he went.John sings as he works.引导时间状语从句的表达：引导时间状语从句的表达：1.As soon as;immediately;directly;the moment;the minute;no soonerthan;hardly/scarcelywhen;once（表示（表示“一一.就就.”）2.Till;until;notuntil（表示（表示“直直到到才才.”）3.before 表示表示“在在.之前就之前就”;since（表示（表示“自从自从.到现到现在为止在为止”）4.Every time;each time;next time;the first time;any time;all the time（表示（表示“每次；下一次；第一次；每次；下一次；第一次；任何时候；总是任何时候；总是”）1.-Why didnt you tell him about the meeting?-He rushed out of the room _ I could say a word.(2006四川四川)A.before B.until C.when D.after2.“You cant have this football back _ you promise not to kick it at my cat again,”the old man said firmly.(2006广东广东)A.until B.when C.since D.because3.A dozen ideas were considered _ the chief architect decided on the design of the building.(2006上海上海)A.because B.before C.whether D.unless4.-How long do you think it will be _ China sends a manned spaceship to the moon?-Perhaps two or three years.(2006福建福建)A.when B.until C.that D.before5.He was about halfway through his meal _ a familiar voice came his ears.(2006辽宁辽宁)A.why B.where C.when D.while6.How can you expect to learn anything _ you never listen?(2006山东山东)A.in case B.even if C.unless D.whenGRAMMAR 2GRAMMAR 2The past perfect tenseThe past perfect tenseThe past perfect tense is used to talk about actions that happened before something else in the past.1.Before Ringo _(join)the Beatles,he _(play)drums in another band.Complete these sentences with the verbs in brackets.2.Before they _(tour)America,the Beatles _(become)stars in their own country.3.Before they _(record)Let It Be,the Beatles _(record)eleven other albums.4.After they _(record)Let It Be,the band _(split up).5.After the group _(split up),all the Beatles _(perform)as solo artists.1.Unfortunately,he _(leave)at the show after I _.(arrive)Complete these sentences with the verbs in brackets.2.By the time we _(arrive)at the stadium,the band _(begin)playing.3.Fortunately,the power cut _(happen)after the fans _(leave)the stadium.4.Before he _(record)his latest album,he _(make)some songs with Paul McCartney.Galileo is known _ his theory of falling objects _ the world _ a scientific pioneer.be known as be known for be known to强调句型的结构强调句型的结构陈述句：陈述句：It is+_that(who)_It is+_that(who)_一般疑问句一般疑问句：Is it+_that(who)_Is it+_that(who)_特殊疑问句特殊疑问句：疑疑问词+is it that_+is it that_ It was with great joy_he received the news that his lost daughter had been found.A.because B.which C.since D.thatHe is a man of few words.It is only after has had a few drinks _ he can open up.A.when B.as C.that D.which _ he will return to his native land.A.It is long before that B.It is before long that C.It wont be long before D.It will be long before that.-You seem to have been impressed by his songs.-Well,not exactly so.It was his way of singing rather than his voice _ really impressed me.A.that B.what C.which D.itShe did quite well in her written papers;it was in the oral examination _ she fell down.A.who B.whom C.that D.whyIt is what you do rather than what you say _ matters.A.that B.what C.which D.thisIt wasnt until nearly a month later _I received the managers reply.A.since B.when C.as D.thatIt was _back home after the experi