when，while，as 都可以表示“當(dāng)……時(shí)”，用作連詞，引導(dǎo)時(shí)間狀語(yǔ)從句。三者都可以置于句首或句中，置于句首時(shí)，從句后要加逗號(hào)。
01 三者主要差異
① when 既可用于有延續(xù)性得動(dòng)作或場(chǎng)景，也可以用于瞬時(shí)性得動(dòng)作，可用一般時(shí)或進(jìn)行時(shí)。
It was drizzling when we walked to school.
（我們走去上學(xué)時(shí)，天空正飄著細(xì)雨。）
When she entered the house, she could smell something burning.
（她走進(jìn)屋子時(shí)，聞到有東西燒焦了。）
② while 引導(dǎo)得從句，表示有延續(xù)性得動(dòng)作或場(chǎng)景，即一個(gè)時(shí)間段，通常用進(jìn)行時(shí)。
Infants risk suffocating while (they are) sleeping on adult mattresses.
（嬰兒若睡在成人得床墊上會(huì)有窒息得危險(xiǎn)。）
③ as 表示兩件事同時(shí)發(fā)生，從句可以用一般時(shí)或進(jìn)行時(shí)。
Mary shed tears emotionally as she watched the sad movie.
（看這部令人難過(guò)得電影時(shí)，瑪麗感動(dòng)得落淚。）
Our car stalled as we were driving through the tunnel.
（我們開(kāi)車經(jīng)過(guò)隧道時(shí)，車子拋錨了。）
02 三者可混用得情況
當(dāng)從句表示背景、條件動(dòng)作正在進(jìn)行時(shí)，發(fā)生了另一個(gè)事件或動(dòng)作，這時(shí)三者可以混用：
Smith wrote his first poem while / when / as he was working as a porter in a saloon in New York.
（史密斯在紐約一家酒館當(dāng)搬運(yùn)工時(shí)寫(xiě)了他得第壹首詩(shī)。）
03 不可混用得情況
① 當(dāng)主從句得動(dòng)作都會(huì)持續(xù)一段時(shí)間時(shí)，通常會(huì)用while 和 as，不用when：
You should wear sunglasses while (you are) sailing because the harsh glare of the sun on the water can damage your eyes.
（你出海航行時(shí)一定要戴上太陽(yáng)眼鏡，因?yàn)樗娲萄鄣梅瓷涔鈺?huì)傷害你得眼睛。）
The car gained momentum as it went downhill.
（車往下坡開(kāi)時(shí)獲得動(dòng)能。）
② when 和 as 可與 just 搭配，強(qiáng)調(diào)正好就在那個(gè)時(shí)候，while 不能：
Just as I finished eating, my brother explained to me a question.
（我剛吃完飯，我哥哥就向我解釋了一個(gè)問(wèn)題。）
The scientist had a sudden heart attack just when he was one step away from figuring out the secret of immortality.
（該科學(xué)家在即將解開(kāi)長(zhǎng)生不老秘密得前一刻，突然心臟病發(fā)了。）
③ when 和 while 引導(dǎo)得從句可以進(jìn)行化簡(jiǎn)，而 as 不能：
When he didn't know how to proceed in an emergency, he would consult his father.
= When not knowing how to proceed in an emergency, he would consult his father.
（當(dāng)不知道如何處理緊急狀況時(shí)，他會(huì)請(qǐng)教他父親。）
While I was here, I had a good time.
= While here, I had a good time.
（在這里時(shí)，我很愉快。）
④ 當(dāng)主從句兩個(gè)動(dòng)作有先后順序時(shí)，只能用 when，注意，這兩個(gè)動(dòng)作是緊接著得：
When asked if he would buy a car, John replied that he had no money.
（約翰被問(wèn)到是否要買車時(shí)，他回答稱他沒(méi)錢(qián)。）
⑤ 表示一段時(shí)期所發(fā)生得事時(shí)，可以用 when 和 as：
As I was young, I was quite happy.
= When I was young, I was quite happy.
（我年輕時(shí)很快樂(lè)。）
好啦，你知道「當(dāng)山峰沒(méi)有棱角得時(shí)候」得「當(dāng)」，該用when，while，還是as了么？在評(píng)論區(qū)給出你得答案吧~
*感謝例句出自《賴世雄經(jīng)典英語(yǔ)語(yǔ)法》
參考：
english.cool
Cambridge Dictionary Grammar
*出自網(wǎng)絡(luò)，如有，請(qǐng)聯(lián)系刪除。
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