如何区分when是做从属连词还是并列连词?They were having a meeting when I got there.这句 书上说是从属连词,可是我看也像并列连词啊.

如何区分when是做从属连词还是并列连词?They were having a meeting when I got there.这句 书上说是从属连词,可是我看也像并列连词啊.
如何区分when是做从属连词还是并列连词?
They were having a meeting when I got there.这句 书上说是从属连词,可是我看也像并列连词啊.

如何区分when是做从属连词还是并列连词?They were having a meeting when I got there.这句 书上说是从属连词,可是我看也像并列连词啊.
并列连词 when 和引导时间状语从句的从属连词 when 是不同的.这主要表现在以下几个方面：
1.位置：when 引导时间状语从句时,该从句可放在主句之前也可放在主句之后；而并列连词 when 只能位于两个分句之间,而且前面常常有逗号.例如：
Come when you please.
你高兴来就来吧.（ when 为从属连词）
When I saw him,he was writing to a friend of his.
我看见他时,他在给一个朋友写信.（ when 为从属连词）
I was taking a walk,when I came across him.
我正在散步,突然碰见了他.
2.意义：when 作从属连词用时,它所引导的从句表示主句中谓语动词动作发生的时间,即作“当……时”解；而并列连词 when 连接的两个分句中,第一个分句表示的是背景,第二个分句表示的是一种突然的、意想不到的情况或过早发生的事情.when 通常含“这时突然”之义.例如：
I was thinking of this,when I heard my name called.
我正想着这件事,突然听到有人叫我的名字.
I had just fallen asleep,when the boor-bell rang.
我刚入睡,门铃突然响了起来.
这种意义在孤立的句子中可以理解到,在文章中更能体会得到.如在“ I was wandering through the street when I caught sight of a tailor's shop ”一句中,“在街头漫步”只是“看见有家缝纫店”的时间,其后作者怎样走进缝纫店,想要什么样的衣服,怎样受到伙计的奚落,又怎样受到老板的奉承等情景均与“漫步街头”没有直接的因果关系.
3.时态：when 引导的时间状语从句中可以根据句意的需要用一般现在时、一般过去时、过去进行时、分别说明现在,过去,甚至将来的行为；并列连词 when 后面的分句中通常用非延续性动词的一般过去时,其前表时间的分句中可用：
（ 1 ）过去进行时表示过去某时间正在进行的动作.例如：
I was cooking when I heard her knocking at the door.
我正在做饭,突然听到她敲门的声音.
He was thinking about the problem,when an apple fell to the ground.
他正在思考这个问题,突然有一只苹果掉到了地上.
（ 2 ） was /were going to,was / were about to,was / were on the point of 表示过去某一时间将要发生的动作.例如：
I was just going when he came in.
我正要走,这时他就进来了.
We were about to start when it began to rain.
我们刚要动身天就开始下起雨来了.
He was on the point of leaving,when someone knocked at the door.
他刚要走就有人敲门.
（ 3 ）过去完成时表示过早发生的事情.请看下述两种场合：
（ a ）过去完成时和含否定意义的 hardly,scarcely,nearly 连用,和 just,little 连用,或者与否定词 not 连用时,表示“刚……,就……”的意思.例如：
I had hardly opened the door when he hit me.
我刚一开门他就打了我一下.
I had nearly reached the town,when the young man suddenly said very slowly,“ Do you speak English?”我快要进城了,年轻人突然慢慢地说：“你会讲英语吗?”
I had been there little more than a week when I set to work in earnest.
我到那儿还不超过一个星期就开始认真干起活来.
I had not been reading for half an hour when I heard steps outside.
我读了还不到半个钟头就听到外面有脚步声.
（ b ）过去完成时与 hardly 等连用时,when 也可以换成 before .例如：
Hardly had I left before the trouble started.
我刚一离开麻烦就开始了.
4.句型：when 引导状语从句时,主句可以是肯定句,也可以是疑问句形式,但 when 连接两个并列分句时,其前的分句只能是肯定句,即只能是不带否定副词 not 的分句.前文（ 3 ）（ a ）最后一个例句算是一个例外.试比较：
Mick was sleeping when they went in.（并列句）迈克正在睡觉,他们突然走了进来.
When they came in Mick was sleeping.（主从句）他们进来时迈克正在睡觉.
“ Was Mick sleeping when they came in?”和“ What was Mick doing when they came in?”只能是对其中主句的提问,因为这时 when 所引导的分句既无突然性也不是句子中的未知信息,而只是另一个动作发生的特定时间