As, when和while均为连接词。在一些情况下，As, when和while的用法相近，但在其他情况下，三者也会有略微的差别。今天小厚就带大家一起来看一看这三个词的用法吧~
Another family arrived as we were leaving.
When my father was out working in the field, I helped with milking the cows, feeding the pigs.
While he was working, he often listened to music.
我们也可以用as, when和while + 过去进行时，用来表示背景事件:
As she was leaving the court, a crowd of photographers gathered around her.
Steven was very unhappy when things weren’t going well for him.
Lucy came into the room while he was waiting.
As she walked to the door, she thanked them for a lovely dinner.
As they were signing the contract, they noticed that a page was missing.
He was walking back to his flat when he heard an explosion.
根据上下文，when既可以表示“after”的意思，也可以表示“at the same time”的意思：
When（=After）you open the file, check the second page.
I eat popcorn when I am watching TV. （=at the same time）
The phone always rings just when I’m closing the front door.
We spent long evenings talking in my sitting-room while he played the music he had chosen and explained his ideas.
We were lying on the beach sunbathing while they were playing volleyball.