③ though, although, even if, whatever等引导的让步状语从句

④ as, than引导的比较状语从句

⑤ as, as if, as though引导的方式状语从句

遵循的原则

         当从句与主句的主语或宾语一致，且从句谓语为be时，可将从句主语及be省略。

         当从句的主语是it，且从句谓语含有be时，可将it及be省略。

         当so或not代替上文内容，此时可有if + so/not句式

常见的结构

         连词(as, as if, once)+名词

         连词(though, whether, when)+形容词

         连词(whether, as if, while)+介词短语

         连词(when, while, though)+现在分词

         连词(when, if, even if, unless, once, until, than, as)+过去分词

         连词(as if, as though)+不定式

e.g.  Once (he was) a teacher, he now works in a government office.

          Work hard when (you are) young, or you’ll regret.

          He looked everywhere as if (he was) in search of something.

          While (I was) walking along the street, I heard my name called.

          The exhibition is more interesting than (it was) expected.

          He opened his lips as if (he were) to speak.

          Her father told her to be careful when (she was) crossing the street.

          Unless (it is) necessary, you’d better not refer to the dictionary.

          Get up early tomorrow. If not (= If you don’t get up early), you will miss the first bus.

          He may not be at home then, if so (= if he is not at home), leave him a note.

4．从属连词的多义性

【探究小课堂】

探究主题 如何掌握部分从属连词的多义性

探究材料 Why do you want a new job ______ you've got such a good one already?

　　A . that B . where C . which D . when

探究导航 正确答案是D。此题考查的是从属连词 when 的用法。但是通过题干意义可知，这里的 when 并不是我们平时常用的意义“当……的时候”，而是“既然”的意思，相当于“since”。其实从属连词中有不少象when 这样的词，具有多义性。本文就这一问题作一归纳。

一、when

　　1 . 表示时间，意思是“当……的时候”。例如：　　

　　The fire was put out when they came. 他们来到的时候，大火已经被扑灭了。

　　2 . 表示条件，意思是“如果……，要是……”例如：

　　When the weather is good, I usually go to the country.

　　Turn off the switch when anything goes wrong with the machine.

　　3 . 表示原因，意思是“既然”。例如：

　　How can he succeed when he won't work?

　Why do we take the flag down at night, when we just have to put it up again in the morning?

　　4 . 表示让步，意思是“虽然，然而，可是”。例如：

　　He walks when he might ride .

　　We have only three chairs when we need five .

二、while　

　　1 . 表示时间，意思是“当……的时候”，“和……同时”。例如：

　　We waited while he dined .

　　Please be quiet while I am talking to you .

　　2 . 表示让步，意思是“虽然，尽管”。例如：

　　While I understand what you say , I can't agree with you .

　　While he is respected , he is not liked .

　　3 . 表示对比，意思是“而，然而”。例如：

　　She is very diligent , while he is very lazy .

　　You like sports , while I'd rather read .

三、If

　　1 . 表示条件或假设，意思是“如果，假如”。例如：

　　We'll stay at home if it rains tomorrow .

　　If I were you , I would not go .

　　2 . 表示让步，意思是“虽然，即使”。例如：

　　I will go if I die for it .

　　If I am wrong