for表因为时怎么用？

表原因时，
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，because引导的是句子中的重要部分，常放在句末。逗号可加可不加。

例：You can trust those products because the quality never changes.
I haven”t been to the cinema lately, because I am too busy.
I didn”t go, because I was afraid.

2）当原因是显而易见的或已为人们所知，就用as或 since。since稍正式一些。
Since /As the weather is so bad, we have to delay our journey.

3） 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：He is absent today, because / for he is ill.
He must be ill, for he is absent today.

because of后面应该加名词，这个具体句子中很好辨析．
例：I don't like him because of his dishonesty.

for表示原因时，置于主句之后,表示非直接的随后附加说明的理由或推断理由。
如： She didn’t go to school, for she was ill.

关于on和about：两者都可作介词，表示“关于”之意。在涉及文章、书籍、演说、报告等有关内容时，二者可通用。如：

a book on ／about the radio一本关于无线电的书

二者的区别在于：
on常用于较正式场合，着重指内容的严肃性、学术性及深度。一般指学术专著。如：
a report on the international sit