先看下面一道高考題:
-I\'m going to the post office.
-________you\'re there, can you get me some stamps?
A. As B. While C. Because D. If
對(duì)連詞的用法考查在每年高考題中均有涉及。Because引導(dǎo)原因狀語(yǔ)從句, If引導(dǎo)條件狀語(yǔ)從句,按題干提供的情景均不可取。While和As都能引導(dǎo)時(shí)間狀語(yǔ)從句,極易混淆。As一般強(qiáng)調(diào)主句謂語(yǔ)動(dòng)詞與從句謂語(yǔ)動(dòng)詞動(dòng)作的同時(shí)性,而While除可表示同時(shí)性外,還含有一個(gè)動(dòng)作在另一個(gè)動(dòng)作正在進(jìn)行或持續(xù)過(guò)程中的某一時(shí)刻發(fā)生。再?gòu)念}干所提供的情景判斷,就可知道B為最佳答案。
while的用法可從下述幾點(diǎn)理解與運(yùn)用。
一、while意為\"當(dāng)......時(shí)候\",指一段時(shí)間,不能用來(lái)表示一個(gè)時(shí)間點(diǎn)。
While the discussion was still going on, George came in. 當(dāng)討論還在進(jìn)行時(shí),喬治走了進(jìn)來(lái)。
二、while意為\"而;然而\",表示轉(zhuǎn)折。
There\'re plenty of rain in the southeast, while there\'s little in the northeast. 東南部雨量充足,而西北部則很少下雨。
三、while意為\"雖然;盡管\",表示讓步。
While I admit his good points, I can see his shortcomings. 盡管我承認(rèn)他的優(yōu)點(diǎn),但我還是能看到他的缺點(diǎn)。
四、while意為\"只要\",表示條件。
We can surely overcome these difficulties while we are closely united. 只要我們緊密地團(tuán)結(jié)一致,一定能克服這些困難。
五、while從句中的省略。
當(dāng)while從句中的主語(yǔ)與主句的主語(yǔ)一致,且含有be的某種形式時(shí),從句中的主語(yǔ)連同be可同時(shí)省略。
While listening to the radio, she fell asleep. 她在聽(tīng)收音機(jī)時(shí)睡著了。
While in London, he studied music and painting. 在倫敦時(shí),他學(xué)習(xí)音樂(lè)和繪畫(huà)。
六、while可用作名詞,意為\"一會(huì)兒;一段時(shí)間\"。
作名詞用時(shí),主要用于短語(yǔ)中: after a while \"過(guò)了一會(huì)兒\"; all the while \"一直,始終\"; a short / little while ago \"剛才\"; once in a while \"偶爾,間或\"; wait / rest(for) a while \"等 / 休息一會(huì)兒\"。
I haven\'t seen her for a long while.我好久沒(méi)有看見(jiàn)她了。
Where have you been all this while?這一陣子你到哪去了?
He usually goes to work by bike, but once in a while he goes by bus. 他通常騎自行車(chē)上班,但偶爾也乘公共汽車(chē)。
I looked everywhere for the letter, but it was in my pocket all the while. 我到處找那封信,卻不知它一直在我口袋里。
七、while與when以及as之間的區(qū)別。
1. 當(dāng)從句中的謂語(yǔ)動(dòng)詞是持續(xù)性的動(dòng)作時(shí),我們可以用while, when或as。
While / When / As I was walking down the street, I noticed a police car in front of the bank.我順著馬路往前走時(shí),發(fā)現(xiàn)銀行門(mén)前停著一輛警車(chē)。
2. 當(dāng)從句中的謂語(yǔ)動(dòng)詞表示瞬間動(dòng)作時(shí),不可用while。
He was on the point of leaving when someone knocked at the door. 他正要走,這時(shí)有人敲門(mén)。
3. 如果談?wù)搩蓚€(gè)長(zhǎng)動(dòng)作,最常用的是while。
While John was sitting biting his nails, I was working out a plan to get us home. 約翰坐在那里咬指甲時(shí),我想出了一個(gè)回家的辦法。
不過(guò), as是可以用來(lái)說(shuō)明兩種正在發(fā)展或變化的情況的,這時(shí)as引導(dǎo)一個(gè)持續(xù)性的動(dòng)作,主句中的動(dòng)作與之同時(shí)進(jìn)行。
As we talked on, he got more and more excited. 我們繼續(xù)往下談的時(shí)候,他越來(lái)越興奮。
4. 如果表示兩個(gè)短動(dòng)作或事件同時(shí)發(fā)生,最常用的是as或just as,也可用when。
Just as he caught the ball, there was a tearing sound. 當(dāng)他抓住球的時(shí)候,有一種撕裂的聲音。
I thought of it just when you opened your mouth. 就在你要說(shuō)話的時(shí)候,我也想到了。

be made of/from 由……制成 
be made of 是可以看得出原料的 
be made from 是不可以看出原料的 
make up of 由……組成 表示“部分構(gòu)成整體”，用于主動(dòng)語(yǔ)態(tài)；如果用整體作主語(yǔ)，必須用被動(dòng)結(jié)構(gòu)be made up of，這時(shí)可以和consist of互換
consisit of 表示“整體由部分組成”，引申為“包含有”，不能用于被動(dòng)語(yǔ)態(tài)