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

　　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)as 表示“当……时”，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”。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.

　　7.引导原因状语从句的从属连词有because，as，since等。

　　because“因为”语气最强，回答why提问时只能用because，其引导的从句可放在句首或句末;as“由于”、since“既然”语气不如because强，引导的从句常置于句首;for是并列连词，语气最弱，对前面分句加以解释或补充说明，其引导的分句常置于句末且用逗号隔开。

　　He didn't go to school because he was ill.

　　As it was raining, we went there by bus.

　　Since everybody is here, let's begin.

　　It must have rained last night, for the ground is wet.

　　注意：because与so不能同时使用。

　　8.引导让步状语从句的从属连词有：although/though(虽然，尽管)，even though/if (即使)

　　Although/ Though it is a very young country, it is very rich.

　　Even if/ though you were here yesterday, you couldn't help him.

　　注意：although/though 引导的从句不能与but连用，但可与yet，still连用。

　　9.引导目的状语从句的从属连词有so that和in order that(以便，为了)等。

　　The teacher spoke loudly so that /in order that we could hear him clearly.

　　10.引导结果状语从句的从属连词有：so that(结果是)和so/such…that…(如此…以至于)等。

　　It was very cold, so that the water in the bowl froze.

　　He got there so early that he got a good seat.

　　It is such a heavy box that nobody can move it.

　　11.引导比较状语从句的连词：as…as…(与…一样)，not as/so… as…(不如)，than(比)等。

　　I know you better than she does.

　　He works as carefully as she.

　　I can't run as/so fast as you.

　　注意：在时间状语从句和条件状语从句中，如果主句是将来时，从句要用一般现在时。

　　I'll go on with the work when I come back tomorrow.

　　He won't come unless he is invited.