when引导的从句的谓语动词可以是延续性的动词，又可以是瞬时动词。并且when有时表示“就在那时”。
例如：
When she came in, I stopped eating.她进来时，我在吃饭。(瞬时动词)
When I lived in the countryside, I used to carry some water for him.当的住在农村时，我常常为他担水。（延续性的动词）
We were about to leave when he came in.我们就要离开，就在那时他进来了。
While引导的从句的谓语动作必须是延续性的，并强调主句和从句的动作同时发生（或者相对应）。并且while有时还可以表示对比。例如：
While my wife was reading the newspaper, I was watching TV. (was reading是延续性的动词，was reading和was watching同时发生)
I like playing football while you like playing basketball.我喜欢踢足球，而你喜欢打篮球。（对比）
as soon as
as soon as 意义为“一…就” ，引导时间状语从句，可置于句首或句末，最常见的用法是在将来时态的情境中，遵守“主将从现”，的原则，i.e.
1. I'll write you as soon as I get there.
我一到那儿，就给你写信。
2. They will post the tickets to me as soon as they receive my cheque.
他们收到我的支票后就立刻把票寄给我.
3.Let us start as soon as he comes.
等他一来我们就动身。
当然也有用在过去时态的情境中，i.e.
I arranged the flowers in the vase as soon as I came back home.
一回到家里，我就把花在花瓶里插好。
As soon as his father went out, the boy ran to the cinema.
爸爸刚出门, 那男孩就跑向电影院。
until在肯定句中,可以和时间状语连用,表示“(动作或状态的继续)一直……为止”。例如:I waited until nine o’clock,andthen I left.我一直等到9点才离开。2.用在否定句中,表示“到……为止”“直到……才”,常与表示瞬间动作的动词连用。
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