while 的用法
1 连词 引导时间状语从句,意为 当.时候 while 引导的句子的谓语部分必须是可以延续的动词或结构.
My mother is cooking while my father is reading the newspaper .
She fell asleep while she was doing her homework .
2 名词 意为 一会儿 after a while for a while
After a while,she came back .
when的用法
when 连词 意为 当...时候 ...这时.引导时间状语从句,与while 不同,when 引导的句子的谓语部分可以是短暂性的也可以是持续性的动词或结构.
She fell asleep when she was doing her homework .
I was walking in the street when I saw a wallet on the ground .
I saw her singing in the room when I passed by her room .
until 的用法
1 until是连词 引导时间状语从句
两个句型：.(肯定句）until....否定句）until .
They worked until it was dark .他们一直工作凌晨一点.
He didn't go until the boy's parents came back .直到那个男孩的父母回来了,他才走.
2 介词 They kept him waiting until o'clock in the afternoon .
