__the teacher came in,all the students were writing.A.Where B.When C.While D.As 为什么选B不选D急用The students were talkingas the teacher came in.为什么就对呢

__the teacher came in,all the students were writing.A.Where B.When C.While D.As 为什么选B不选D急用The students were talkingas the teacher came in.为什么就对呢
__the teacher came in,all the students were writing.A.Where B.When C.While D.As 为什么选B不选D
急用
The students were talkingas the teacher came in.为什么就对呢

__the teacher came in,all the students were writing.A.Where B.When C.While D.As 为什么选B不选D急用The students were talkingas the teacher came in.为什么就对呢
when,while,as的区别和用法
三者可表示“当……时候”,区别如下：
(1) 若主句表示的是一个短暂性动作,从句表示的是一个持续性动作,三者都可用：
He fell asleep when [while,as] he was reading.他看书时睡着了.
【注】as 用于引出一个持续性动词表示“在……期间”时,其谓语通常只能是那些含有动作(action)和发展(development) 意味的动词,一般不能是那些不用于进行时态的动词(如 be,seem,love,want,agree,see,know,have 等),所以下面一句中的 while 不能换为 as：
A：I’m going to the post office.我要去邮局.
B：While you’re there,can you get me some stamps?当你在邮局时,能帮我买几张邮票吗?
(2) 若主、从句表示两个同时进行的持续性动作,且强调主句表示的动作延续到从句所指的整个时间,通常要用 while：
Don’t talk while you’re eating.吃饭时不要说话.
I kept silent while he was writing.在他写的时候,我默不作声.
但是,若主从句表示的两个同时进行的动作含有“一边…一边”之意思,通常用 as：
She sang as she went along.她边走边唱.
(3) 若从句是一个短暂性动作,主句是一个持续性动作,可用 as / when 但不用 while：
It was raining hard when [as] we arrived.我们到达时正下着大雨.
(4) 若主从句表示的是两个同时(或几乎同时)发生的短暂性动作,用 as / when：
I thought of it just when [as] you opened your mouth.就在你要说的时候,我也想到了.
(5) 若要表示两个正在发展变化的情况,相当于汉语的“随着”,一般用 as：
Things are getting better and better as time goes on.随着时间的推移,情况越来越好.
As it grew darker,it became colder.天色越晚,天气越冷.
(6) 表示“每当…的时候”(暗示一种规律性),一般要用 when：
It’s cold when it snows.下雪时天冷.
He smiles when you praise him.你夸奖他时他总是笑笑.
(7) 若主从句所表示的动作不是同时发生,而是有先后顺序时,一般要用 when：
I will go home when he comes back.他回来时,我就回家去.
(8) when 可用作并列连词,表示“这时(突然)”；while 也可以用作并列连词,表示“而”、“却”(表示对比)；但 as 则没有类似用法：
We were about to start when it began to rain.我们正要出发,这时天开始下雨了.
He likes coffee,while she likes tea.他喜欢咖啡,而她却喜欢茶.
(9) as 和 when 后均可直接跟一个名词,构成省略句,但 while 一般不这样用：
As [When] a boy,he lived in Japan.他小时候在日本.
(10) when 和 while 后可接现在分词、介词短语、形容词等构成省略句,但 as 一般不这样用：
When [While] reading,he fell asleep.他看书时睡着了.
When [While] in trouble,ask her for help.遇到麻烦的时候你就去找她帮忙.
我觉得是你没把这几个词的用法弄清楚啊,看看吧,也许会明白的.加油啦!

这是时间状语从句，主句又be doing sth，从句的引导词应该用when

when 是当什么时候的意思，当老师进来时，所有的学生都在写作
as 没有这个意思，可以说不着边

应该是当老师进来时，所有的学生都在写作业。因此，“当”翻译成“when”更为恰当，而“as”在此不合适