许多同学只知道 when 表示“当……的时候”，其实还可以是“尽管”、“虽然”、“既然”、“本该...却..."(对比)、“如果”、“考虑到”的意思。
又虽然He walks when he might take a taxi. 尽管他可以坐出租车，但他却走路。He stopped trying when he might have succeeded next time. 尽管他本来下次就可以成功的了，但他却停止努力了。The boy was restless when he should have listened to the teacher carefully. 这男孩子本来应该专心听老师讲的，但他却坐立不安。这男孩子本来应该专心听老师讲的，但他却坐立不安。
如Come when you are ready. (if)
I can’t tell you anything when you won’t listen.(although)
She stopped trying, when she might succeed next time.(although)
They have only three copies when we need five. (本该...却...)
When the wind blows, all the doors rattle.(whenever)
(D)：Why do you want a new job ______ you’ve got such a good one already?
A. that B. where C. which D. when
He was about to tell me the secret _________ someone patted him on the shoulder.
A. as B. until C. when D. while
分析：答案 C。最大干扰项是A。when 意为“这时(突然)”，主要用于某一动作突然发生于另一动作正在进行或刚要发生之时。此时的 when 可以连用副词 suddenly，也可以不连用它，但值得注意的是，同学们不能单独用 suddenly 来代替 when，如下面各题的答案选A，不选B：
I was about to go out ______ the telephone rang.
A. when B. suddenly C. as soon as D. directly
We were swimming in the lake ______ the storm started.
A. when B. suddenly C. until D. before
She was walking down the road _________ she heard someone shouting for help.
A. when B. suddenly C. until D. before
While引导的从句的谓语动作必须是延续性的，用于时间较长时;并强调主句和从句的动作同时发生(或者相对比 译为‘而’)。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.(对比)
Would buy me some stamps while you are in the post office?
While locked up in prison, she wrote her first novel.
While Mary was writing a letter, the children were playing outside.
As表示“一边……一边”，as引导的动作是延续性的动作?不能是状态动词，一般用于强调主句和从句动作同时发生;as也可以强调“一先一后”、表示对比时，用于发生时间较短时例如：
We always sing as we walk.(as表示“一边……一边”)
As we was going out, it began to snow.(as强调句中两个动作紧接着先后发生，而不强调开始下雪的特定时间) 有时这三个连词可以互换，有时不可以。It was raining hard when (as) I got there.( 动作同时发生，when可换为as, 但不能换为while，因为get是点动词.)
Mother was worried because little Alice was ill, especially as (when/ while) father was away. (此时as ,when, while可通用) while, as不能代替
While the alien was buying a souvenir, the girl called the police. (表示主句，从句的动作同时发生)
She thought I was talking about her daughter, while, in fact, I was talking about my daughter. (表转折，对比，when, as都不能代替它)
2.由before和after引导的时间状语从句。
注意before引导的从句不再用否定式的谓语，主句用将来时，从句总是用现在时;如果before引导的从句谓语用的是过去时，则主句动词多用过去完成时或者一般过去时，根据情况可翻译成“...才....”，“....就....”，“....还没....”，“...趁着....”“然后...." 等。After表示主句动作发生在从句动作之后。主句和从句的动作的时间关系正好与before引导的从句相反。例如：
It will be four days before they come back. (...才....)
It wasn't long before they got arrested by the policemen.(就)
Einstein almost knocked me down before he saw me.(才)
My father had left for Canada just before the letter arrived.(才)
They had not been married four months before they were divorced.(就)
Think before you leap.(然后)
He had gone out of the door before I could say a single word of it.(还没)