AS, WHEN and WHILE are conjunctions. When introducing an adverbial clause of time, AS, WHEN and WHILE can mean the same, but they can also have slightly different meanings.
AS, WHEN, WHILE是连词。AS, WHEN, WHILE在引导时间状语从句时，既有共性，也有不同。
AS:
◆We can use AS to introduce two events happening at the same time. After AS, we can use a simple or continuous form of the verb.
◆AS用来引导两件同时发生的事件，AS从句的动词可用简单时态或进行时态。
★As I was at home, the postman came.
★我在家的时候，邮递员来了。
★As she walked to the door, she thanked them for a lovely dinner.
★在她走到门口的时候，她感谢他们提供的美味晚餐。
★As they were signing the contract, they noticed that a page was missing.
★在签署合同的时候，他们发现少了一页。
★We were lying on the beach sunbathing as they were playing volleyball.
★我们躺在沙滩上晒日光浴时，他们在打排球。
★As I was walking out of the coffee shop, I drop the cup.
★正当我走出咖啡店时，杯子掉了。
◆We prefer AS to talk about two things that change together in time.
◆当表示两件事随着时间同时改变时，我们更倾向于使用AS。
★We do not necessarily grow wiser as we grow older.
★我们未必随着年龄的增长而变得越来越睿智。
★As you eat more, you will gain more weight.
★吃得越多，你的体重就越重。
★As you study more, you will get better grades.
★学习地越多，就会取得更好的成绩。
WHEN:
◆We can use WHEN to introduce a single completed event that takes place in the middle of a longer activity or event. In these cases, we usually use a continuous verb in the main clause to describe the background event.
◆WHEN用来引导在一个较长的活动或事件中，另一个动作已经完成。在这种情况下，主句通常使用一个连续性的动词来描述背景事件。
★He was walking back to his flat when he heard an explosion.
★当他听到爆炸声时，他正在回公寓的路上。
★I was driving my car when suddenly a meteor crashed into the road.
★我正在开车，突然一颗流星撞在路上。
★I was having lunch when Andy arrived.
★安迪到的时候，我正在吃午饭。
★What were you doing when you heard the news?
★当听到这个消息时，你在做什么？
◆We use WHEN to talk about phases of life (not WHILE or AS).
◆讨论生命的各个阶段时，用WHEN，而非WHILE或AS。
★When you were a kid, you used to be so shy.
★当你还是个孩子的时候，你很害羞。
★I read this book when I was in high school.
★我在上高中时读过这本书。
★She loved this movie when she was young.
★她年轻时喜欢这部电影。
◆Use WHEN to tell general truths or things that usually happen.
◆描述事实或经常发生的动作，用WHEN。
★I love drinking orange juice when I am sick.
★我在生病时，喜欢喝橙汁。
★She goes camping when she has time.
★她一有时间就去野营。
◆Sometimes, WHEN has the same meaning as AFTER.
◆有时，WHEN与AFTER同义。
★She cried when/after she heard the news.
★听到这个消息后，她哭了。
★Call me when/after you've finished.
★完成后就打电话给我。
WHILE:
◆WHILE also show two events happen at the same time. After WHILE, we can use a simple or continuous form of the verb.
◆WHILE也可用来引导两个同时发生的动作，WHILE从句的动词可用简单时态或进行时态。
★I always listen to music while I drive.
★我开车时总是听音乐。
★While I buy the bread, you can go to the butcher’s.
★我买面包的时候，你可以去买肉。
★The police stopped him while he was driving.
★他在开车的时候，警察拦住了他。
★Don’t disturb me while I am doing my homework.
★我在做作业的时候，不要打扰我。
◆Use WHILE when you are doing two continuous actions at the same time.
◆连接两个连续性的动作，用WHILE。
★I’m having a bath while reading a book.
★我边洗澡边看书。
★While he was sweeping the floor, Andy was resting.
★他在扫地的时候，安迪在休息。
◆WHILE and WHILST are two words with identical meanings as a conjunction.
◆WHILE, WHILST作连词时，意思完全相同。
★While/ Whilst Andy was sleeping in, his little brother was reading a book.
★安迪在睡懒觉的时候，他的弟弟在读书。
JUST WHEN or JUST AS:
◆We often use JUST WHEN or JUST AS to express things happening at exactly the same time.
◆我们经常用JUST WHEN或JUST AS来表示事情完全同时发生。
★The phone rings just when I’m closing the front door.
★我刚关上前门，电话就响了。
★She was a brilliant gymnast, but she had a terrible accident in 2000, just as her career was taking off.
★她是一名出色的体操运动员，就在她的职业生涯刚刚起步时，却在2,000年遭遇了一场可怕的事故。
★Just as I was falling asleep, somebody called my phone.
★正当我入睡时，有人给我打电话。
We use reductions with WHEN and WHILE省略用法
◆We can use WHEN and WHILE without a verb, or without a subject + auxiliary verb BE. We can’t use AS in this way.
◆WHEN与WHILE引导的从句可以省略动词或者省略主语+助动词be，AS不能这样用。
★Go past the village signpost and you get to a church. When there, take the next turning right.
★穿过村子的路标，你就到了一座教堂。到了那里，在下一个路口右转。
★Tell me when ready.
★准备好后告诉我。
★While a student, I used to live with my family.
★上学的时候，我和家人住在一起。
★He was reading a book while waiting for the bus. (= while he was waiting)
★他边等公共汽车边看书。
★Cover your mouth when coughing. (= when you were coughing)
★咳嗽时要捂住嘴。
★You should eat healthy food while recovering. (= while you were recovering)
★恢复期间应健康饮食。
AS or WHILE:
◆AS and WHILE are used to talk about two longer actions or situations that develop at the same time. They can be used with both simple and continuous tense forms. Simple tenses and continuous tenses show the same meaning.
◆AS和WHILE均可用来引导两个同时进行的持续时间较长的动作。AS和WHILE从句的动词可用简单时态或进行时态。简单时态和进行时态表达的意思相同。
★While I worked in the garage, my wife cooked lunch.
★我在车库工作的时候，我的妻子在做午餐。
★She did the dishes as I cleaned the car.
★我清洗汽车的时候，她在洗碗。
◆But we prefer WHILE when talking about two continuous actions that develop at the same time.
◆但表示两个同时进行的延续性动作，我们更倾向于使用WHILE。
★While I was sweeping the floor, my mother was cleaning the attic. =
★While I swept the floor, my mother cleaned the attic.
★我在扫地的时候，我母亲在打扫阁楼。
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