狀語從句的概念：
狀語從句指句子用作狀語時，起副詞作用的句子。它可以修飾謂語、非謂語動詞、定語、狀語或整個句子。根據(jù)其作用可分為時間、地點、原因、條件、目的、結(jié)果、讓步、方式和比較等從句。狀語從句一般由連詞(從屬連詞)引導(dǎo)，也可以由詞組引起。從句位于句首或句中時通常用逗號與主句隔開，位于句尾時可以不用逗號隔開。
比較while/as/when：
1、as/when引導(dǎo)短暫性動作的動詞例句：
如：Just as/Just when/When I stopped my car, a man came up to me.
2、當(dāng)從句的動作發(fā)生于主句動作之前，只能用when引導(dǎo)這個從句，不可用as或while。
如：When you have finished your work, you may have a rest.
3、從句表示“隨時間推移”連詞能用as，不用when或while。
如：As the day went on, the weather got worse.
比較untill/till：
兩個連詞意義相同,肯定形式表示的意思是“做某事直至某時”，動詞必須是延續(xù)性的。否定形式表達的意思是“直至某時才做某事”，動詞為延續(xù)性或非延續(xù)性都可以。
正確使用這兩個連詞的關(guān)鍵之一就在于判斷句中的動詞該用肯定式還是否定式。
肯定句例句：I slept until midnight. 我一直睡到半夜時醒了。
Wait till I call you. 等著我叫你。
注意：在肯定句中可用before代替：Let's get in the wheat before the sunsets.
否定句例句：She didn't arrive until 6o'clock.
I didn't manage to do it until you had explained how.
1、Until可用于句首，而till通常不用于句首。
例句：Until you told me, I had heard nothing of what happened.
2、Untilwhen疑問句中，until要放在句首。
例句：Until when are you staying? 你呆到什么時候？
注意：否定句可用另外兩種句式表示。
1）Not until…在句首，主句用倒裝。
例句：Not until the early years of the19th century did man know what heat is.
2）It is not until…that…
狀語從句的用種類：
1、時間狀語從句：
表示時間的狀語從句可由when, as, while, whenever, after, before, till(until), since, once, as soon as(或the moment), by the time, no sooner…than, hardly(scarcely)… when, everytime等引導(dǎo)。
e.g. When I came into the office, the teachers were having a meeting.
He started as soon as he received the news.
Once you see him, you will never forget him.
No sooner had I gone to bed than I went to sleep.
2、原因狀語從句：
原因狀語從句是表示原因或理由的，引導(dǎo)這類從句的最常用的連詞是because, since, as, nowthat（既然）等，for表示因果關(guān)系時（它引導(dǎo)的不是從句）為并列連詞，語氣不如because強。 e.g. He is disappointed because he didn't get the position.
As it is raining, I will not go out.
Now that you mention it, I do remember.
3、地點狀語從句：
引導(dǎo)地點狀語從句的連詞是where和wherever等。
e.g. Sit wherever you like.
Make a mark where you have a question.
4、目的狀語從句：
引導(dǎo)目的狀語從句最常用的詞（組）是so, so that（從句謂語常有情態(tài)動詞）, in order that, in case（以防，以免）等。
e.g. Speak clearly, so that they may understand you.
She has bought the book in order that she could follow the TV lessons.
He left early in case he should miss the train.
5、結(jié)果狀語從句：
結(jié)果狀語從句是表示事態(tài)結(jié)果的從句，通常主句是原因，從句是結(jié)果。由so that（從句謂語一般沒有情態(tài)動詞）,so…that, such…that等引導(dǎo)。
e.g. She was ill, so that she didn't attend the meeting.
He was so excited that he could not say a word.
She is such a good teacher that everyone admires her.
6、條件狀語從句：
條件狀語從句分真實性（有可能實現(xiàn)的事情）與非真實性（條件與事實相反或者在說話者看來不大可能實現(xiàn)的事情）條件句。
引導(dǎo)條件狀語從句的詞（組）主要有if, unless, so(as)long as, on condition that, so(as) far as, if only(=if)。
注意：條件從句中的if不能用whether替換。
e.g. If he is not in the office, he must be out for lunch.
You may borrow the book so long as you keep it clean.
So far as I know（據(jù)我所知）, he will be away for three months.
You can go swimming on condition that(=if) you don't go too far away from the river bank.
If he had come a few minutes earlier, he could have seen her.
7、讓步狀語從句：
讓步狀語從句可由although, though, as, even if(though), however, whatever, whether…or, no matter who(when, what,…)等引導(dǎo)。
注意：as引導(dǎo)的讓步狀語從句一般是倒裝的。
e.g. Though he is a child, he knows a lot.
Child a she is, he knows a lot.
Whatever(=No matter what) you say, I'll never change my mind.
8、方式狀語從句：
方式狀語從句常由as, as if(though), the way, rather than等引導(dǎo)。
e.g.You must do the exercise as I show you.
He acted as if nothing had happened.
9、比較狀語從句：
比較狀語從句常用than, so(as)…as, the more…the more等引導(dǎo)。
e.g. I have made a lot more mistakes than you have.
He smokes cigarettes as expensive as he can afford.
The busier he is, the happier he feels.
使用狀語從句時要注意的幾個問題：
1、在時間和條件（有時也在方式、讓步等）從句中，主句是一般將來時，從句通常用一般現(xiàn)在時表示將來。
e.g. We'll go outing if it doesn't rain tomorrow.
I'll write to you as soon as I get to Shanghai.
2、有些時間、地點、條件、方式或讓步從句，如果從句的主語與主句主語一致（或雖不一致，是it），從句的謂語又包含動詞be，就可省略從句中的“主語+be”部分。
e.g. When(hewas) still a boy of ten, he had to work day and night.
If(you are) asked you may come in.
If(it is) necessary I'll explain to you again.
3、注意區(qū)分不同從句：引導(dǎo)的是什么從句，不僅要根據(jù)連詞，還要根據(jù)句子結(jié)構(gòu)和句意來判別。以where為例，能引導(dǎo)多種從句。
e.g. You are to find it where you left it.（地點狀語從句）
Tell me the address where he lives.（定語從句，句中有先行詞）
I don't know where he came from.（賓語從句）
Where he has gone is not known yet.（主語從句）
This place is where they once hid.（表語從句）
注意：表示“一…就…”的結(jié)構(gòu) hardly/scarcely…when/before/no sooner…than和as soon as都可以表示“一…就…”的意思。
例句：I had hardly/scarcely got home when it began to rain.
I had no sooner got home than it began to rain.
As soon as I got home, it began to rain.
注意：如果hardly/scarcely或nosooner置于句首，句子必須用倒裝結(jié)構(gòu)：
例句：Hardly/Scarcely had I got home when it began to rain.
No sooner had I got home than it began to rain.