4.表示因果关系的并列连词有：for(因为)，so(所以)。

He is not at school today, for he has a bad cold.

It was late, so I went home.

5.引导时间状语从句的从属连词有：before, after, when, while, as, till, until, since, as soon as等。

After they had planted their crops, they took a rest.

We have learned six lessons since he began to teach us.

As soon as he gets to Beijing, he’ll call me.

1) when, while, as 都表示“当……时”，when从句谓语动词既可以是瞬间动词也可以是延续性动词，可用于主从句动作同时发生或从句动作先于主句动作发生。while从句谓语动词只能是延续性动词，侧重主从句动作同时发生。as引导一个持续性动作，多用于主从句动作同时发生，强调“一边……一边”。

When I came in, my father was cooking.

I came in when/while my father was cooking.

He sang as he walked.

2)until用法：当主句谓语动词是延续性动词时，主从句都用肯定式，译为“直到……为止”;当主句谓语动词是瞬间动词时，主句用否定式，从句用肯定式，即not…..until, 译为“直到……才”。

Mr. Green waited until his children came back.(格林先生一直等到他的孩子们回来)

Mr. Green didn’t go to bed until his children came back. (格林先生直到他的孩子们回来才睡觉)

6. 引导条件状语从句的从属连词有：if(如果), unless(除非，如果……不)等。

If you don’t go soon, you’ll be late.=Unless you go soon, you’ll be late.

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