状语从句
I、时间状语从句
一、when，while和as
1．When既可引导一个持续动作，也可引导一个短暂动作，可用于主句和从句动作同时发生或从句动作先于主句动作.如：
When I lived there, I used to go to the seashore on Sundays.我住在那里时，星期天常到海滨去.
When the film ended, the people went back. 电影一结束，看电影的人便回去了.
当when引导的时间状语从句为系表结构，而且其主语和主句的主语一致，其表语又是一个名词时，就可以用以as引出的省略句，来代替when引出的从句.As a you man （=When he was a young man），he was fond of hunting.
他年轻时，喜欢打猎.
2．While引导的动作必须是持续的，侧重主句动作和从句动作相对比.如：
Please don’t talk so loud while others are working别人在工作时，别高声谈话.
While I was wondering at this, our schoolmaster took his place. 正当我对此不解时，我们校长就座了.
3. as引导一个持续性动作，多用于主句和从句动作同时发生.如：
He hurried home, looking behind as he went. 他匆匆忙忙跑回去一边走一边回头望.
John sings as he works 约翰一边工作，一边唱歌.
4. when还可用作并列连词，其意义为“那时，这时”，相当于at this/ that time. 常用于下列句式：
Somebody was doing s omething when…
Somebody was about to/ going to do something when…
Somebody had just done something when….
如：We were having a meeting when someone broke in
We were about to set off on our way, when it suddenly began to rain.
此外When还表示原因“既然”.如：
It was foolish of you to make a taxi when you could easily walk there in five minutes.
5.while作为并列连词，意为“而，却”，表示对比.
He likes pop music, while I am fond of folk music.
6．如果主句表示的是短暂动作，而从句用延续性动作的进行时态表示在一段时间内正在进行的动作时，when, while 与as可互换使用.如：
When/ While/ As I was walking down the street, I came across an old friend of mine.
二、as soon as, immediately, directly, the moment, the minute, no sooner…than…, hardly/ scarcely…when…, once（一旦...
就...）
这些从属连词引导的从句表示从句的动作一发生，主句的动作随即发生，常译为“一...就...”.从句中一般时态代替将来时态.如：
Once you remember it, you’ll never forget it.
The moment I heard the voice, I knew father was coming.
No sooner had we arrived at the station than the train left.
The boy burst into tears immediately he saw his mother.
▲注意：No sooner…than, hardly/ scarcely…when…这一结构的时态搭配no sooner与hardly/ scarcely引导的主句谓语动词应用过去完成时，而than与when的从句中谓语应用一般过去时，此外，当把no sooner和hardly/ scarcely 提到句首时，应用倒装语序.
I had hardly got home when it began to rain.→Hardly had I got home when it began to rain.
三、till, until和not…until
1．肯定句：主句谓语动词必须是延续性动词，主句、从句都为肯定式，意为“某一动作一直延续到某点时间才停
止”.如：
He remained there until she arrived. 他一直留到她来.
You may stay here until the rain stops. 你在这里可呆到雨停.
2．否定句：主句谓语动词必须是非延续性动词，从句肯定式，意为“某动作直到某时间才开始”.如：He won’t go to bed till (until) she returns. 直到她回来他才睡.
3．till不可以置于句首，而until可以.如：
Until you told me I had no idea of it. 直到你告诉我，我才知道这件事.
4．Not… until句型中的强调和倒装说法：
It was not until you told me that I had any idea of it.（强调句型）
Not until you told me did I have any idea of it.（not until置于句首主句要倒装）
四、before和since
1．若表达“还未...就...”“不到...就...”“...才...”“趁，还没来得及”时，需用连词before.如：We had sailed four days and four nights before we saw land. 我们航行了四天四夜才看到陆地.
We hadn’t run a mile before he felt tired. 我们跑了还不到一英里他就累了.
Please write it down before you forget it. 趁你现在没忘把它记下来.
Before I could get in a word, he had measured me.我还没来得及插话他就给我量好了尺寸.
▲before从句中谓语不用否定式.又如：
Before they reached the station the train had gone. 他们（还没）到火车站前，火车已开走了.
2．It will be + 段时间before sb does. “多久之后才...”.如：
It will be half a year before I come back.
I won’t be long before we meet a gain.
3．Since从句的谓语动词一般是非延续性动词，主句的谓语动词是延续性的或者是反复发生过的动作.Since从句的时态若是一般过去时，相应地，主句中的时态是现在完成时或现在完成进行时.如：
I have written home four times since I came here. 自从我到这里来，我往家写了四封信.
She has been working in this factory since she left school.
4．在It is +时间+since从句句型中，时间的计算一律从since从句的动作完成时态或状态结束时算起.如：It is three years since the war broke out.
战争爆发以来，有三年了.
It is three years since she was in our class.
她离开我们班有三年了.
It is three years since he lived here
他不在这里住有三年了.
It is three years since I (have) smoked a cigar.(=since I stopped smoking a cigar)我不吸烟有三年了.
如果译成“我吸烟有三年了.”应为：It is three years since I began to smoke.
5．Every time, each time, next time, the first time, any time, all the time等名词短语用来引导时间状语从句，表示“每当...，每次...，下次...”.如：
Every/ Each time I was in trouble, he would come ti help me out.
Next time you come, do remember to bring your son here.
The last time she saw James, he was lying in bed. 她最后一次看到詹姆士时，他躺在床上.
The first time I climbed onto the wall, I felt nervous.
You are welcome to come back any time you want to. 你想回来时随时可回来.
II、地点状语从句
1．引导地点状语从句的从属连词有：where，wherever指具体地点时，从句可用于主句之前或之后，表示抽象条件的含义时，从句需放在主句之前.如：
We should go where the Party needs us most.
