语法复习专题（13）状语从
    1、时间状语从句
    （1）as、when、while用法一览表。
类别
作    用
例    句
as
as表示“当……的时候”，往往和when/ while通用，但它着重强调主句与从句的动作或事情同时或几乎同时发生。
include of 用法She came up as I was cooking.(同时)
The runners started as the gun went off.(几乎同时)
when
(at or during the time that )既可以表示在某一点的时候，又可表示在某一段时间内，主句与从句的动作或事情可以同时发生也可以先后发生。
It was raining when we arrived.(指时间点)
When we were at school, we went to the library every day.(在一段时间内)
while
while意思是“当……的时候”或“在某一段时间里”。主句中的动作或事情在从句中的动作或事情的进展过程中发生，从句中的动词一般要用延续性动词。在when表示a period of time时，两者可以互换。
Please don’t talk so loud while others are working.
He fell asleep while/when reading. Strike while the iron is hot.(用as或when不可，这里的while意思是“趁……”)

（2）引导时间状语从句的连接词除上述外还有：
①till, not …  until …, until, before, since
Don’t get off the bus until it has stopped.
He waited for his father until(till)it was twelve o’clock.
It will be five years before he returns from England.
②hardly / scarcely … when, no sooner … than, as soon as once
表示“一……就”
As soon as I have finished it , I’ll give yu a call.
Once you show any fear, he will attack you.
We had hardly got / Hardly had we got into the country when it
began to rain.
No sooner had he arrived / He had no sooner arrived than she started complaining.
③directly, immediately, the moment, the minute that… 一……就
He made for the door directly he heard the knock.
④each time, every time, by the time
Each time he came to my city, he would call on me.
注意：表示未来情况，主句用将来时，从句用现在时。
2、让步状语从句
（1）although与though可以引导让步状语从句，不能与but连用，但可以与yet连用。
Although they are poor,(yet)they are warm-hearted.
（2）even if或even though引导让步状语从句，表示“即使”，“纵然”，用来使人注意下文所强调内容的性质。
I’ll get there even if(though)I have to sell my house to get enough money to go by air.
（3）no matter后接上who、what、where、how等疑问词，也可以在这类疑问词后面加上ever构成whoever、whatever、wherever、however等。
Don’t trust him, no matter what / whatever he says.
Whoever breaks the law will be published.
No matter how hard the work is, you’d better try to do it well.
（4）as也可以引导让步状语从句。要用倒装。
Child as(though)he is, he knows a lot.
Much as I like it, I won’t buy.
Try as he would, he couldn’t lift the heavy box.
3、原因状语从句：because, for, as, since, now that
（1）表示不知道的原因时用because,即说话人认为听话人不知道，因此because从句是全句最重要的部分，通常它被置于主句之后。
You want to know why I’m leaving? I’m leaving because I’m full.
for虽然表示不知道的原因，但其语气较because要弱得多，是可说可不说的话，它只能置于主句之后，这时，for是并列连词。如果不是因果关系，而是对前面主句的内容加以解释或推断时，只能用for。如：It’s morning now, for the birds are singing.（很显然，鸟叫不可能是“现在已是早上”的原因。）
（2）表示已经知道的原因时用as或since,即某种原因在说话人看来已经很明显，或已为听话人所熟悉，因此它是句中不很重要的部分。since要比as正式一些，它们通常被置于语句之前，但有时却相反。
Seeing all of the children already seated, he said,“Since everyone is here, let’s start.”
(3)下列情况下只能使用because:
①在回答why的问句时；
②在用于强调句型时；
③被not所否定时。
4、地点状语从句：where, wherever
Make a mark wherever you have any questions.
We will go where the Party directs us.
5、目的状语从句：that, so that, in order that
注意：目的状语从句的谓语动词常与情态动词连用，否则可能是结果状语从句。不可置于句首。
6、结果状语从句：that, so that, so … that, such … that …
注意：so + 形容词/副词 + that从句；such +　名词 + that从句。
7、方式状语从句：as, as if(though)
I’ll do as I am told to.
It looks as if it is going to rain.
8、比较状语从句：than, as
9、条件状语从句：if, unless, so (as) long as, in case, once, a far as, on condition that.
注意if与unless的区别：不能用and连接两个unless从句，即不能有… unless …,and unless … 。但if … not and if … not却不受此限。
You won’t lose your weight unless you eat less and unless you exercise more.(×)
但可以说 … unless you eat less and exercise more.
10、注意状语从句中从句的省略现象
（1）连接词 + 过去分词
Don’t speak until spoken to.
Pressure can be incrased when needed.
Unless repaired, the washing machine is no use.
（2）连词 +　现在分词
Look out while crossing the street.
（3）连词 + 形容词/其他
常见的有it necessary、if possible、when necessary、if any等。
选择填空
1. I don’t think I’ll need any money but I’ll bring some ____________.
(NMET  2000)
A.as last        B.in case        C.once again        D.in time
解析：答案为B。句意为“带些钱以防万一”，只能选择in case。引导的条件状语从句，后面省略了I should need it。
2. The WTO can’t live up to its name _________ it doesn’t include a country that is home to one fifth of mankind.（NMET  2000）
A.as long as      B.while        C.if        D.even though
解析：答案为C。本题考查状语从句的用法。句意为“假如世贸组织不包括占世界人口五分之一的中国的话，那它就名不副实”。as long as语气过于强烈，while和even though不符合句意。
3、Someone called me up in the middle of the night, but they hung up_________I could answer the phone.(NMET  2000)

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