【考点解读】
在复合句中，修饰主句或主句谓语的句子叫作状语从句。状语从句可位于主句之前，也可位于主句之后。状语从句可分为时间、地点、原因、结果、条件、方式、让步、比较和目的等九大类。
一、状语从句引导词列表
从句类型从属连词
时间状语从句as, after, before, once, since, till, until, when, whenever, while, as soon as
地点状语从句where, wherever, anywhere, everywhere
原因状语从句because, since, as, now (that), seeing that, considering that, in that
结果状语从句that, so that, so/such ...that ...
目的状语从句so that, in order that, for fear that, in case, for the purpose that
条件状语从句if, unless, as/so long as, on condition that, in case, provided that
比较状语从句than, as ...as, not so/as ...as
方式状语从句as, as if/though, how
让步状语从句though, although, even if/though, however, whatever, as, while
【点睛】
(1)上述有些连词除了能引导状语从句外，还可引导定语从句和名词性从句。在使用的时候，要根据句子结构和句意来判别和区分不同的从句，正确使用引导词。以where为例，试比较下列多种从句的区别。
You are to find it where you left it. (地点状语从句)
Tell me the address where he lives. (定语从句，先行词为the address)
I don’t know where he came from. (宾语从句)
Where he has gone is not known yet. (主语从句)
This place is where they once hid. (表语从句)
(2)在两个分句间要有一个且只有一个连词，千万不能按汉语习惯。
Because he was ill, he didn’t come to school.
＝He was ill, so he didn’t come to school.
(3)在时间、地点、条件、方式或让步状语从句中，若从句的主语与主句的主语一致(或从句的主语为it)，从句的谓语又包含动词be时，从句中的“主语＋be”部分可省略。
When (he was) asked about it, he kept silent.
Fill in the blanks with articles when (they are) necessary.
If (it is) possible, I’ll explain it again later.
She stood at the gate as if (she was) waiting for someone.
二、时间状语从句
1. “一……就……”的表达如下表
2. till和until的用法
(1)肯定句中，主句谓语动词必须是延续性动词，意为“某一动作一直延续到某时间点才停止”。
He remained there till/until she arrived.
(2)否定句中，主句谓语动词必须是非延续性动词，从句为肯定式，意为“某动作直到某时间才开始”。
I was not aware that I forgot my ticket till/until I got to the station.
(3)till不可置于句首，until可以。
(4)强调和倒装句中，not ...until应视为一个整体，同时被强调或置于句首。
It was not until you told me that I had any idea of it.
Not until you told me did I have any idea of it.
3. before和since的用法
(1)before常用于表示“还未……就；不到……就；……才；趁……；还没来得及”等含义。
We had sailed four days and four nights before we saw land.
He rushed out of the house before I could say anything else.
(2)句型It was/will be＋时间段＋before ...意为“过了多久才……”。It was not long before ... /It will not be long before ...意为“不久就……”。
It will be one year and a half before I come back.
It was not long before he sensed the danger of the position.
(3)since从句的谓语动词一般是短暂性动词，主句谓语动词则是延续性动词或反复发生的动作。since 引导的从句时态为一般过去时，主句时态为现在完成时或现在完成进行时。
She has been working for the company since she left school.
(4)句型It is/has been＋时间段＋since ...意为“自从……到现在多久了”。
It is a long time since I saw you last time.
＝ I have not seen you for a long time.
It has been two years since I was admitted to this key middle school.
＝ I was admitted to this key middle school two years ago.
It is three years since I smoked a cigar.
＝ It is three years since I stopped smoking a cigar.
三、原因状语从句
1. because, as, since, now that的用法区别如下表：
—Why are you absent from the meeting? —Because I am ill.
He is disappointed because he didn’t get the position.
As his mother was a great music lover, he lived with music from birth.
Since his music style was new, he decided his hairstyle had to be new too!
2. 除了状语从句外，一些介词短语也可以表示原因。如：because of, thanks to, due to, owing to, on account of等。
They were late because of the traffic.
3. for引导表示原因的并列句，补充说明根据什么推断出前一分句的结果。
He must have gone to bed, for the light is out.
