when,while,as,justas表示当的时候用法上有什么区别

Question

when,while,as,just as表示当的时候用法上有什么区别

Answer 1

1.当从句中的谓语动词是持续性的动作时,我们可以用while,when或as.
While / When / As I was walking down the street,I noticed a police car in front of the bank.我顺着马路往前走时,发现银行门前停着一辆警车.
2.当从句中的谓语动词表示瞬间动作时,不可用while.
He was on the point of leaving when someone knocked at the door.他正要走,这时有人敲门.
3.如果谈论两个长动作,最常用的是while.
While John was sitting biting his nails,I was working out a plan to get us home.约翰坐在那里咬指甲时,我想出了一个回家的办法.
不过,as是可以用来说明两种正在发展或变化的情况的,这时as引导一个持续性的动作,主句中的动作与之同时进行.
As we talked on,he got more and more excited.我们继续往下谈的时候,他越来越兴奋.
4.如果表示两个短动作或事件同时发生,最常用的是as或just as,也可用when.
Just as he caught the ball,there was a tearing sound.当他抓住球的时候,有一种撕裂的声音.
I thought of it just when you opened your mouth.就在你要说话的时候,我也想到了.
at last / in the end / finally
三者都可作“最后；终于”解,但用法有所不同.
at last只能指时间位置,而不能指时间顺序,在语义上指经过,周折,等待,耽搁后的“最后,终于”得到所期待的结果.
1 At last ,he passed the exam .最后他终于通过了考试.（可用in the end代替）
2 His chance came at last.他的机会终于来了.（强调他为获得此机会进行的各种努力.）
3 The war had been long and hard,but now there was peace at last.
经过漫长而艰苦的战争,现在和平终于到来了.
finally 指一系列事物或论点的顺序,在列举事物时可以用来引出最后一项内容 finally 在意义上与用法上与at last 有共同之处,但也有不同.finally 既可指时间位置（相当于at last和in the end）,也可指时间的先后顺序.finally 有两个用法：一是在列举事物或论点时,可用来引出最后一项内容；二是用在句中动词前面,表示“等了好久才……”.
eg.Finally I’d like to thank you all for your coming .最后我要感谢诸位的光临.（不能用at last）
2 They waited and waited ,and the concert finally started.他们等啊等啊,最后音乐会终于开始了.
3 Three policemen rode past on their motorbikes ,then came the TV broadcasting car and finally the Marathon runners.三个警察骑着摩托过去了,接着来了电视广播车,最后过来的是马拉松赛跑选手.
in the end 表示结局,有时可与at last 换用,不同的是in the end 也可以用于指将来时,其余两个则不行.
（1）All will come right in the end .到头来一切都会好的.
（2）He tried many times to pass the examination ,and in the end he succeeded.他多次努力想通过考试,最后成功了.