19.1 地点状语从句
地点状语从句通常由where, wherever 引导。例如：
Where I live there are plenty of trees. 我住的地方树很多。
Wherever I am I will be thinking of you. 不管我在哪里我都会想到你。
19.2 方式状语从句
方式状语从句通常由as, (just) as…so…, as if, as though引导。
1)as, (just) as…so…引导的方式状语从句通常位于主句后，但在(just) as…so…结构中位于句首，这时as从句带有比喻的含义，意思是\"正如…\"，\"就像\"，多用于正式文体。例如：
Always do to the others as you would be done by. 你希望人家怎样待你，你就要怎样待人。
As water is to fish, so air is to man. 我们离不开空气，犹如鱼儿离不开水。
Just as we sweep our rooms, so we should sweep backward ideas from our minds.
正如打扫房屋一样，我们也要扫除我们头脑中落后的东西。
2)as if, as though
两者的意义和用法相同，引出的状语从句谓语多用虚拟语气，表示与事实相反，有时也用陈述语气，表示所说情况是事实或实现的可能性较大。汉译常作\"仿佛……似的\"，\"好像……似的\"。例如：
They completely ignore these facts as if (as though) they never existed. 他们完全忽略了这些事实，就仿佛它不存在似的。(与事实相反，谓语用虚拟语气。)
He looks as if (as though) he had been hit by lighting. 他那样子就像被雷击了似的。(与事实相反，谓语用虚拟语气。)
It looks as if the weather may pick up very soon. 看来天气很快就会好起来。(实现的可能性较大，谓语用陈述语气。)
说明：as if / as though也可以引导一个分词短语、不定式短语或无动词短语。例如：
He stared at me as if seeing me for first time. 他目不转睛地看着我，就像第一次看见我似的。
He cleared his throat as if to say something. 他清了清嗓子，像要说什么似的。
The waves dashed on the rocks as if in anger. 波涛冲击着岩石，好像很愤怒。
19.3 原因状语从句
比较because, since, as和for：
1)because语势最强，用来说明人所不知的原因，回答why提出的问题。当原因是显而易见的或已为人们所知，就用as或 since。例如：
I didn\'t go, because I was afraid. 我不去是因为我怕。
Since /As the weather is so bad, we have to delay our journey. 天气那么糟，旅行推迟了。
2)由because引导的从句如果放在句末，且前面有逗号，则可以用for来代替。但如果不是说明直接原因，而是多种情况加以推断，就只能用for。例如：
He is absent today, because / for he is ill. 他今天缺席，因为他病了。
He must be ill, for he is absent today. 他一定病了，所以今天缺席。
19.4 目的状语从句
表示目的状语的从句可以由that, so that, in order that, lest, for fear that, in case等词引导。例如：
You must speak louder so that /in order that you can be heard by all. 你必须大点声，别人就能听见了。
He wrote the name down for fear that(lest) he should forget it. 他写下了这个名字以免以后忘记。
Better take more clothes in case the weather is cold. 最好多穿点衣服，以防天发冷。
19.5 结果状语从句
结果状语从句常由so…that 或 such…that引导。so…that与such…that之间可以转换。例如：
The boy is so young that he can\'t go to school. 这男孩年龄太小，不能上学。
He is such a young boy that he can\'t go to school
19.6 条件状语从句
连接词主要有 if, unless, as/so long as, on condition that 等。if 引导的条件句有真实条件句和非真实条件句两种。非真实条件句已在虚拟语气中阐述。
unless = if not. 例如：
Let\'s go out for a walk unless you are too tired. 如果不太累，我们去散散步。
If you are not too tied, let\'s go out for a walk.
典型例题
You will be late ___ you leave immediately.
A. unless B. until C. if D. or
答案A。句意：除非你立即走，否则你就回迟到的。可转化为 If you dong leave immediately, you will be late。B、D句意不对，or表转折，句子如为 You leave immediately or you will be late.