because表示人们不知道的直接的原因或理由，着重点在从句，其所引导的从句，为全句句意的中心所在。通常用于回答why引出的疑问句，语气最强，除特别强调外，该从句一般位于主句后面。
I didn t go ａｂｒｏａｄ with her because I couldn t afford it.
我没有和她一起出国是因为费用太高。
Don t scamp your work because you are pressed for time.
不要因为时间仓促而马马虎虎。
as引导的原因状语从句所传递的通常是已知信息，从句多位于主句之前，通常可以和since换用。如： As I didn t know the way，I asked a policeman.
我不认识路，因而问警察。
As it is snowing, we shall not climb the mountain.
由于在下雪，我们不去爬山了。
(3) since引导的原因状语从句
since引导的原因状语从句所传递的通常是已知信息，从句多位于主句之前，通常可以和as换用。如： Since traveling by air is much faster,they decided to take a plane.
既然乘飞机旅行快得多，他们就决定坐飞机。
Since you won t help me ，I ll ask someone else.
你既然不帮我，那我就请别人帮忙。
4. 目的状语从句
in order that“为了；以便”。多用于正式文体，通常可以与so that换用。如：
You stopped at Hangzhou in order that they could go around West Lake.
他们在杭州停了下来，以便游览西湖。
The expert spoke slowly in order that everyone should understand.
专家讲得很慢，以便人人听得懂。
so that“为了；以便”。so that通常可以与in order that换用，它所引导的目的状语从句总是放在主句之后，在非正式文体中，常省略that。如：
Speak clearly so that they may understand you.
你要讲得清楚，他们才听得懂。
She wanted tea ready at seven so she could be out by eight.
她要七点钟备好茶点，这样她八点以前就可以出门了。
５. 结果状语从句
(1) so that引导的结果状语从句
① so that引导的结果状语从句只能位于主句之后，中间可以有逗号。如：
Suddenly it began to rain heavily，so that it was almost impossible to carry on driving.
突然下起了大雨，几乎无法继续开车。
Linda phoned me in on arrival so that I know she was safe and sound.
琳达到达后给我打了电话，因而我知道她平安无事。
②“so that”既可引导结果状语从句也可引导目的状语从句。究竟是引导的结果状语从句还是目的状语从句，除了根据句意来判断外，还可根据结构形式来加以判断。若从句前有逗号，一般为结果状语从句，如果从句中有情态动词，通常则为目的状语从句。如：
They started out early, so that they didn t miss the train.
他们早早就出发了，所以没误火车。(结果状语从句)
They started out early so that they would not miss the train.
他们早早出发是为了不误火车。(目的状语从句)
