過去進(jìn)行時(shí)
過去進(jìn)行時(shí)表示過去某一時(shí)刻或者某段時(shí)間正在進(jìn)行或發(fā)生的動(dòng)作，常和表過去的時(shí)間狀語(yǔ)連用，如：
1. I was doing my homework at this time yesterday.
　 昨天的這個(gè)時(shí)候我正在做作業(yè)。
2. They were waiting for you yesterday.
　 他們昨天一直在等你。
3. He was cooking in the kitchen at 12 o'clock yesterday.
　 昨天12點(diǎn)，他正在廚房燒飯。

過去進(jìn)行時(shí)的構(gòu)成：
肯定形式：主語(yǔ)+was/were+V-ing
否定形式：主語(yǔ)+was not (wasn't)/were not (weren't)+V-ing
疑問形式：Was/Were+主語(yǔ)+V-ing。

基本用法：
1. 過去進(jìn)行時(shí)表示過去某一段時(shí)間或某一時(shí)刻正在進(jìn)行的動(dòng)作。常與之連用的時(shí)間狀語(yǔ)有，at that time/moment, (at) this time yesterday (last night/Sunday/week…), at+點(diǎn)鐘+yesterday (last night / Sunday…)，when sb. did sth.等時(shí)間狀語(yǔ)從句，如：
　　1）What were you doing at 7p.m. yesterday?
　　　昨天晚上七點(diǎn)你在干什么？
　　2）I first met Mary three years ago. She was working at a radio shop at the time.
　　　我第一次遇到瑪麗是在三年前，當(dāng)時(shí)她在一家無(wú)線電商店工作。
　　3）I was cooking when she knocked at the door.
　　　她敲門時(shí)我正在做飯。

后通常用表示暫短性動(dòng)詞，while后通常用表示持續(xù)性動(dòng)詞，而while所引導(dǎo)的狀語(yǔ)從句中，謂語(yǔ)動(dòng)詞常用進(jìn)行時(shí)態(tài)，如：When the car exploded I was walking past it. = While I was walking past the car it exploded.
用作并列連詞時(shí)，主句常用進(jìn)行時(shí)態(tài)，從句則用一般過去時(shí)，表示主句動(dòng)作發(fā)生的過程中，另一個(gè)意想不到的動(dòng)作發(fā)生了。如：
I was walking in the street when someone called me.
我正在街上走時(shí)突然有人喊我。

作并列連詞，表示“（這時(shí)）突然”之意時(shí)，第一個(gè)并列分句用過去進(jìn)行時(shí)，when引導(dǎo)的并列分句用一般過去時(shí)。如：
　　1）I was taking a walk when I met him.
　　　我正在散步，突然遇見了他。
　　2）We were playing outside when it began to rain.
　　　我們正在外邊玩，這時(shí)下起雨來了。

過去進(jìn)行時(shí)和一般過去時(shí)的用法比較：
　　1）過去進(jìn)行時(shí)表示過去正在進(jìn)行的動(dòng)作，而一般過去時(shí)則表示一個(gè)完整的動(dòng)作。
　　例如：They were writing letters to their friends last night.
　　　　　昨晚他們?cè)趯懶沤o他們的朋友。（沒有說明信是否寫完）
　　　　　They wrote letters to their friends last night.
　　　　他們昨晚寫了信給他們的朋友。（表達(dá)了他們已寫好的意思，整個(gè)寫的過程已完成。）
　　2）當(dāng)動(dòng)作延續(xù)較長(zhǎng)時(shí)間時(shí)或表示厭煩、贊美等感情色彩時(shí)，常用過去進(jìn)行時(shí)表示。
　　例如：He was thinking more of others than of himself.
　　　　　他考慮別人的比考慮自己的多。（表示說話者贊揚(yáng)的口氣）
　　　　　The boy was always making trouble then.
　　　　　那時(shí)，他總是惹麻煩。（表示說話者厭煩的口氣）
3. 狀語(yǔ)從句:
　　在復(fù)合句中，修飾主句的動(dòng)詞,形容詞或副詞等的從句叫做狀語(yǔ)從句。狀語(yǔ)從句根據(jù)它表達(dá)的意思可分為時(shí)間、原因、條件、比較、目的、結(jié)果和讓步等類型。
　　 (根據(jù)考試說明,前四個(gè)要求掌握,其它要求理解)
　　時(shí)間狀語(yǔ)（常由下列從屬連詞引導(dǎo)）
　　 when, as ,while (當(dāng)……時(shí)候； 一邊…… 一邊……；在……期間)，
　　 before(在……之前)， after (在……之后)， as soon as（一…… 就…… )
　　 since (自從……時(shí)起到現(xiàn)在)， till/until (直到……時(shí)) 等
例如：
　　1）When my cousin came yesterday, I was playing volleyball.
　　　昨天我表哥來的時(shí)候，我在打排球。
　　2）When the air moves, it is called wind.
　　　空氣流動(dòng)，就產(chǎn)生風(fēng)。
　　3）As the boys walked along the lake, they sang happily.
　　　這些男孩一邊沿湖邊走，一邊愉快地唱歌。
　　4）While I was sleeping, the UFO arrived.
　　　當(dāng)我在睡覺時(shí)，UFO到達(dá)了。

when和while引導(dǎo)時(shí)間狀語(yǔ)從句的區(qū)別：
when表示“當(dāng)……的時(shí)候”。從句中既可用延續(xù)性動(dòng)詞，又可用非延續(xù)性動(dòng)詞，這些動(dòng)詞既可以表示動(dòng)作，又可表示狀態(tài)。從句中的動(dòng)作既可和主句的動(dòng)作同時(shí)發(fā)生，又可在主句的動(dòng)作之前或之后發(fā)生。
例如：Mary was having dinner when I saw her.
　　　　　The boy was still sleeping when his mother got home yesterday morning.
　　　　　When the teacher came in, the students stopped talking.
while表示“在……的時(shí)候”、“在……期間” 、“一邊……一邊……”。while從句中必須是表示動(dòng)作或狀態(tài)的延續(xù)性動(dòng)詞。它強(qiáng)調(diào)主句的動(dòng)作與從句的動(dòng)作同時(shí)發(fā)生或主句的動(dòng)作發(fā)生在從句的動(dòng)作過程中。
例如：The weather was fine while we were in Beijing.
　　　She called while I was out.
　　　I was drawing while my brother was reading.
　　　He likes reading a newspaper while he is waiting for the bus.
如果主句的動(dòng)作在從句的動(dòng)作過程中發(fā)生，從句常用進(jìn)行時(shí)。
例如：While we were swimming, someone stole our clothes.
　　　Don't talk so loud while others are working.

有時(shí)when 和while 可以轉(zhuǎn)換使用。
例如：The girl was watching TV when the alien got in.
when和while引導(dǎo)的時(shí)間狀語(yǔ)從句與這一時(shí)態(tài)連用。所以區(qū)別when和while的用法成了這一單元的難點(diǎn)。
（一）、when，while都有“當(dāng)……時(shí)候”的意思。
when既可表示某一點(diǎn)時(shí)間，也可以表示某一段時(shí)間 。在when引導(dǎo)的時(shí)間狀語(yǔ)從句中，其謂語(yǔ)動(dòng)詞可以是延續(xù)性的，也可以是非延續(xù)性的，可與主句中的謂語(yǔ)動(dòng)詞同時(shí)發(fā)生，也可在其后發(fā)生。
例如： 1、I was just reading a book when she came into my room.
她走進(jìn)我房間時(shí)，我正在看書。
2、Were you writing when the teacher came in?
老師進(jìn)來的時(shí)候，你在寫信嗎？
3、When he was a child he was always trying out new ideas.
他小時(shí)候就常常試驗(yàn)一些新的設(shè)想。

（二）、while只能表示某一段時(shí)間，不能表示某一點(diǎn)時(shí)間。在while引導(dǎo)的時(shí)間狀語(yǔ)從句中，其謂語(yǔ)動(dòng)詞只能是延續(xù)性的，而且也只能與主句中的謂語(yǔ)動(dòng)詞同時(shí)發(fā)生或存在。
例1、While Jim was mending his bike, Lin Tao came to see him.
正當(dāng)吉姆修自行車時(shí)，林濤來看他。
2、You can’t do your homework while you’re watching TV.
你不能一邊看電視一邊做家庭作業(yè)。

（三）、另外，when和while的區(qū)別還在于：while引導(dǎo)的時(shí)間狀語(yǔ)從句多用進(jìn)行時(shí)態(tài)，而when引導(dǎo)的時(shí)間狀語(yǔ)從句多用一般時(shí)態(tài)。
例如：
1、While they were talking , the bell rang.
正在他們談話的時(shí)候，上課鈴響了。
2、I was doing my homework when my mother came back home yesterday evening.
昨天晚上媽媽回家的時(shí)候，我正在做家庭作
通過觀察，我們可以這樣理解：when引導(dǎo)的從句里動(dòng)作發(fā)生的時(shí)間相對(duì)主句動(dòng)作發(fā)生的時(shí)間要短些；while引導(dǎo)的從句里的動(dòng)作發(fā)生的時(shí)間相對(duì)主句而言更長(zhǎng)些。

引申講解：
When，While，As引導(dǎo)時(shí)間狀語(yǔ)從句的區(qū)別
when，while，as顯然都可以引導(dǎo)時(shí)間狀語(yǔ)從句，但用法區(qū)別非常大。
一、when可以和延續(xù)性動(dòng)詞連用，也可以和短暫性動(dòng)詞連用；而while和as只能和延續(xù)性動(dòng)詞連用。
① Why do you want a new job when you’ve got such a good one already？（get為短暫性動(dòng)詞）你已經(jīng)找到如此好的工作，為何還想再找新的？
②Sorry，I was out when you called me．（call為短暫性動(dòng)詞）對(duì)不起，你打電話時(shí)我剛好外出了。
③Strike while the iron is hot．（is為延續(xù)性動(dòng)詞，表示一種持續(xù)的狀態(tài)）趁熱打鐵。
④ The students took notes as they listened．（listen為延續(xù)性動(dòng)詞）學(xué)生們邊聽課邊做筆記。

二、when從句的謂語(yǔ)動(dòng)詞可以在主句謂語(yǔ)動(dòng)作之前、之后或同時(shí)發(fā)生；while和as從句的謂語(yǔ)動(dòng)作必須是和主句謂語(yǔ)動(dòng)作同時(shí)發(fā)生。
1．從句動(dòng)作在主句動(dòng)作前發(fā)生，只用 when。
①When he had finished his homework，he took a short rest．（finished先發(fā)生）當(dāng)他完成作業(yè)后，他休息了一會(huì)兒。
②When I got to the airport，the guests had left．（got to后發(fā)生）
當(dāng)我趕到飛機(jī)場(chǎng)時(shí)，客人們已經(jīng)離開了。
2從句動(dòng)作和主句動(dòng)作同時(shí)發(fā)生，且從句動(dòng)作為延續(xù)性動(dòng)詞時(shí)，when，while，as都可用。
①When ／While ／As we were dancing，a stranger came in．（dance為延續(xù)性動(dòng)詞）當(dāng)我們跳舞時(shí)，一位陌生人走了進(jìn)來。
②When ／While ／As she was making a phone call，I was writing a letter．（make為延續(xù)性動(dòng)詞）當(dāng)她在打電話時(shí)，我正在寫信。
3．當(dāng)主句、從句動(dòng)作同時(shí)進(jìn)行，從句動(dòng)作的時(shí)間概念淡化，而主要表示主句動(dòng)作發(fā)生的背景或條件時(shí)，只能用 as。這時(shí)，as常表示“隨著……”；“一邊……，一邊……”之意。
① As the time went on，the weather got worse．（as表示“隨著……”之意）
② The atmosphere gets thinner and thinner as the height increases．
隨著高度的增加，大氣越來越稀薄。
③As years go by，China is getting stronger and richer．
隨著時(shí)間一年一年過去，中國(guó)變得越來越富強(qiáng)了。
④The little girls sang as they went．小姑娘們一邊走，一邊唱。
⑤The sad mother sat on the roadside，shouting as she was crying．
傷心的媽媽坐在路邊，邊哭邊叫。
4．在將來時(shí)從句中，常用when，且從句須用一般時(shí)代替將來時(shí)。
①You shall borrow the book when I have finished reading it．在我讀完這本書后，你可以借閱。
②When the manager comes here for a visit next week，Ill talk with him about this．下周，經(jīng)理來這參觀時(shí)，我會(huì)和他談?wù)劥耸隆?br>
三、when用于表示“一……就……”的句型中（指過去的事情）。
sb．had hardly（＝scarcely） done sth．when．．．＝Hardly ／ Scarcely had sb．done sth．when．．．
①I had hardly ／scarcely closed my eyes when someone knocked at the door．＝Hardly ／ Scarcely had I closed my eyes when someone knocked at the door．我剛一閉上眼，就有人在敲門了。
②I had hardly ／scarcely entered my room when the telephone rang．＝Hardly ／Scarcely had I entered my room when the telephone rang．
我剛一走進(jìn)房門，電話就響了。
When\while\as的區(qū)別
①when是at or during the time that, 既指時(shí)間點(diǎn)，也可指一段時(shí)間；
while是during the time that，只指一段時(shí)間，因此when引導(dǎo)的時(shí)間狀語(yǔ)從句中的動(dòng)詞可以是終止性動(dòng)詞，也可以是延續(xù)性動(dòng)詞，而while從句中的動(dòng)詞必須是延續(xù)性動(dòng)詞。
②when 說明從句的動(dòng)作和主句的動(dòng)作可以是同時(shí)，也可以是先后發(fā)生；while 則強(qiáng)調(diào)主句的動(dòng)作在從句動(dòng)作的發(fā)生的過程中或主從句兩個(gè)動(dòng)作同時(shí)發(fā)生。
③由when引導(dǎo)的時(shí)間狀語(yǔ)從句，主句用過去進(jìn)行時(shí)，從句應(yīng)用一般過去時(shí)；如果從句和主句的動(dòng)作同時(shí)發(fā)生，兩句都用過去進(jìn)行時(shí)的時(shí)候，多用while引導(dǎo)，如：
a. When the teacher came in, we were talking.
當(dāng)此句改變主從句的位置時(shí)，則為：
While we were talking, the teacher came in.
b. They were singing while we were dancing.
④when和while 還可作并列連詞。when表示“在那時(shí)”；while表示“而，卻”，表對(duì)照關(guān)系。如：
a. The children were running to move the bag of rice when they heard the sound of a motor bike.
孩子們正要跑過去搬開那袋米，這時(shí)他們聽到了摩托車的聲音。
b. He is strong while his brother is weak.
他長(zhǎng)得很結(jié)實(shí)，而他弟弟卻很瘦弱。
具體你可以參考這一段。