状语从句状语从句修饰主句/主句的谓语。
一般有九大类：表示时间、地点、原因、目的、结果、条件、让步、比较和方式等。
时间状语从句1. 用when引导：when表示“当……时候”。
如：Things were different when I was a child. 我小时候情况与现在不同。
People breathe more slowly when they are asleep. 人睡觉时呼吸比较缓慢。
2. 用while引导：while表示“当……时候”。
如：We must strike while the iron is hot. 我们要趁热打铁。
I went swimming while the others played tennis. 我去游泳，其余的人都打网球去了。
注意：while 所引导的时间状语从句中谓语动词必须是持续性的，不能是短暂性的。
3. 用as引导：as表示“当……时候”“随着”。
如：He dropped the glass as he stood up. 他站起来时，把杯子摔了。
We get wiser as we get old. 随着年岁的增长，我们也变得聪明些了。
4. 用before引导：before表示“在……之前”。
如：Turn off the lights before you go to bed. 睡觉前要关灯。
Before he went to university he was a worker. 上大学之前他是工人。
5. 用after引导：after表示“在……之后”。
如：I will tell you after they leave. 他们走我再告诉你。
After you finish the letter show it to me．信写完后给我看看。
6. 用until / till引导：until / till表示“直到……”。
如：He waited until she was about to leave. 他等着一直到她准备离开。
I watched him until he disappeared in the distance. 我瞧着他直到他在远处消失。
这类句型的主句动词通常只能是延续性动词，不能是终止性动词。
但是，在否定句中，主句动词可以是终止性动词，此时构成not…ntil [till]…句式，意为“直到……才……”。
如：She didn’t marry until she was over fifty. 她直到五十多岁才结婚。
We’d better not go until your sister arrives. 我们最好等你姐姐到了再走。
7. 用since引导：since表示“自从……以来”。
如：We have known each other since we were children. 我们从小认识。
They’ve moved twice since they got married. 他们结婚后已搬了两次家。
这类句子的主句通常用现在完成时。
但是，当主句表示一段时间时，可用一般现在时代替现在完成时。
如：It’s a long time since we met last. 好久没见面了。
How long is it since you came in London? 你来伦敦有多久了?地点状语从句地点状语从句多由where或wherever引起：原因状语从句：原因状语从句多由because，as，since，seeing(that)，considering that等连词引起：他英语是讲得很好的。
以利用。
目的状语从句表示目的状语的从句可以由that（以便），so that（以便），in order that（为了；以便），Lest（免得；唯恐），in case(以防)，for fear that（生怕；以免）等引导。
Lucy puts on her new skirt that she can receive others’ praise.Lucy为了获得他人的赞美，穿上了她的新裙子。
Mr Black eats four bowls of rice a day so that he can keep strong.为了保持强壮，Mr Black每天吃四碗饭。
I went to bed early in order that I could get up early.为了早起，我早早地就睡觉了。
I carried a bag of food lest there are no shops around.以防周围没有商店，我带了一包食物。
Lee takes more money in case the price of items is too high.以防物价太高，Lee带了很多钱。
He ran home as fast as he can for fear that it rains.他飞快地往家跑，生怕下雨。
结果状语从句结果状语从句表示主句动作的结果，通常由so…that…或such…that…引导，例如：a) I am so angry that I cannot speak a word. 我气的说不出话来。
b) I am such an angry man that I cannot speak a word. 我气的说不出话来。
细心的同学一定发现，so…that…和such…that…之间的微妙区别了吧？So后面加形容词或副词，而such后面要加名词或名词词组。
例如：a) He is so young that he can't go to school.他还太小不能上学。
b) He is such a young boy that he can't go to school.他还太小不能上学。
除此之外，so that也可以引导结果状语从句，例如：a) I got up late this morning so that I missed the bus. 我早上起晚了，没看上公交。
有时候，so that可以省略其中的so或that。
例如：a) I got up late this morning so I missed the bus.b) I got up late this morning that I missed the bus.条件状语从句常用引导词：if, unless, as/so long as 只要, only if只要, providing/provided that 假如, supposing that, in case that, on condition that。
条件状语从句的基本用法1、用if引导：if意为“如果”。
例句：If you cheat in the exam you’ll never get away with it. 考试作弊必予追究。
2、用unless引导：unless的意思是“如果不”“除非”。
例句：Unless you go at once you will be late. 如果你不马上走，就会迟到的。
3、用as [so] long as引导：as [so] long as的意思是“如果”“只要”。
例句：I’ll remember that day as long as I live. 只要我活着，我就不会忘记那个日子。
4、用in case引导：in case用连词引导条件状语从句时，其意为“如果”“万一”。
例句：In case I forget, please remind me about it. 万一我忘记，请提醒我一下。
5、条件状语从句的时态：当主句为将来时态或含有将来意义时，条件状语从句习惯上要用一般现在时表示将来意义，而不能直接使用将来时态。
eg. I don’t know if it will rain tomorrow. But if it rains tomorrow, I’ll stay at home.不知道明天是否会下雨，但要是下雨的话，我就呆在家里。
让步状语从句引导让步状语从句的连词主要有以下这些：though,although,while,as; even if,even though; whether...or...; no matter+疑问词，疑问词-ever，regardless of+名词/名词短语/名词从句，despite，in spite of。
① though，although：“虽然，纵然”，这两个连词意思大致相同，在一般情况下可以互换使用。
在口语中，though较常使用，although比though正式，二者都可与yet，still或nevertheless 连用，但不能与but连用。
eg. I will go to school though it's too late now.Although he was exhausted, he(still) kept on working.Although/Though he is very old, (yet) he is quite strong.② as（though）：“虽然…但是”，“纵使…”，as引导的让步状语从句必须以部分倒装的形式出现，被倒装的部分可以是表语、状语或动词原形，though也可用于这样的结构中。
eg. Object as/though you may, I’ll go.(=Though/Although you may object, I’ll go.) Fast as you write, you can’t finish your paper in only one night.Lover of towns as I am, I realize that I owe a debt to my early country life.③ whether：“无论，不论，不管”，由这一个复合连词引导的让步状语从句旨在说明正反两方面的可能性都不会影响主句的意向或结果，所以它的语气是比较强烈的。
eg. You'll have to attend the ceremony whether you're free or busy.Whether you believe it or not, it's true.Whether or not you like her, you have to become her husband.④ no matter+疑问词=疑问词-ever：“……都……；不管……都……”eg. No matter what happened, he would not mind. =Whatever happened, he would not mind.⑤ whether...or...：“不论是否……”，“不管是……还是……”eg. Whether you are rich or poor, the end result is the same, death比较状语从句引导比较状语从句的从属连词为as...as，not as/so...as，than，the more...the more 等等，这些都是用来进行比较对比，并且通常会与比较级最高级等连用。