for since because as 当 因为讲时都有什么不同？

because:因为.强调直接原因.
since:因为.强调双方已知无需用说明的事由.
for:因为.强调一种推测.但不一定是事实.
as:强调一般因果关系.用于句首.

Because she's ill,she can't go to my home.因为她病了,所以她没有来我家.
注:because后接句子,而because of后接短语.
Since everyboby is here,let's begin our meeting.
既然大家都到了,那就开始开会吧.
Day breaks,fro the birds are singing.
因为鸟儿在唱歌了,天可能亮了.
As he was not well,i decided to go without him.
由于他身体不太好,我决定不带他去.