he went to sleep quite late（本讲要点为什么不能说）

按照中学教学进度，学完并列连词就是学习引导状语从句的从属连词了。状语从句的种类繁多，连词用法也比较复杂，让我们讨论它们用法的重点和难点。

首先是引导时间状语从句的连词，它们有：after， before， until/till， when，while ，as，as soon as， hardly…when ，no sooner…than，once，since，whenever等。

1.before除了有“在…之前”的意思，还有 “在…之后”、“没…, 不到… ”这样的含义。

在…之前：You should think more <before you do it>.

在…之后 ：It will be four days <before they come back>.

四天后回来=在回来之前四天

= They will not come back <until four days later/after 4 days>.

没…,不到… They had not been married for four months <before they were divorced>.

结婚后不到四个月就离了。

The boys (had) rushed out <before the bell rang>. 铃还没响

2.until有两种含义：“直到…才”和“一直…到”

1）短暂动词只能与“not...until”连用。

直到…才：He didn't go to bed <until 11:30>. 11:30才上床睡觉

不能说：He went to bed <until 11:30>. 上床上到11:30

2）持续动词既能用于肯定，又能用于否定，但表示的时间概念不一样。

直到…才： He didn't study <until 11:30>. 持续动词，11:30才学习

一直…到： He studied <until 11:30>. 持续动词，一直学习到11:30

3.when, while, as 的区别。

1）各有特定含义，三者不能互换。

（1）表示(正)在…这时(just then)，只能用when。

We were about to start <when it began to rain>. 正要出发，这时天下雨

We were having lunch <when he came in>. 正在吃饭，这时他来了

经验之谈：两个过去动作同时发生，相对持续的用过去进行时，相对短暂的用一般过去时。

（2）表示“而、在...同时“或对照、对比，只能用while。

“在...同时 ： <While he loves his students>, he is very strict with them. 爱学生的同时要求严格 =He loves his students，|| but he is very strict with them.

对照、对比：You like tennis <while I'd rather hike>. 他喜欢...而我...，不同主语。

（3）表示”一边…一边“或”随着“ ，只能用as。

She sang <as she worked>. 她一边工作一边唱歌。

You will grow wiser <as you grow older>. 随着年龄的增长变得明智

2）表示“当...的时候”，when, while, as都可用，但要注意谓语动词的特点。

（1）when从句的动作可前可后、可同时，动词可持续、可短暂。

<When they got there>, the train had left.

I loved maths <when I was at school>.

（2）while从句的动作只能是持续动作，且同时发生。

<While he was in Beijing>, he visited the Great Wall.

We can learn <while we work>.

（3）as从句的动作同时，动词可持续、可短暂。

I saw him <as he was getting off the bus>.