The boss asked the secretary to hurry up with the letters so that he could sign them.

　The teacher raised his voice on purpose that the students in the back could hear more clearly.

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。例如：

He got up so early that he caught the first bus.

It's such a good chance that we must not miss it.

To such an degree was he excited that he couldn't sleep last night.

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

　She is as bad-tempered as her mother.

　The house is three times as big as ours.

　The more you exercise, the healthier you will be.

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.

We'll start our project if the president agrees.

　You will certainly succeed so long as you keep on trying.

　Provided that there is no opposition, we shall hold the meeting here.

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。

Examples：

(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)