for,since ,because的区别

1.because表示直接原因,它所指的原因通常是听话人所不知道的,其语气最强.常用来回答why的提问,一般放于主句之后,也可以单独存在.例如：
(1)I stayed at home because it rained.因为下雨我呆在家里.
(2)Because Lingling was ill,she didn”t come to school.玲玲因病,没有上学.
(3)A:Why is she absent?她为什么缺席?
B:Because she is sick.因为她病了.
此外,在强调句型中,只能用because.例如：
(4)It was because I missed the early bus that I was late for school.我上学迟到是因为我没有赶上早班汽车.
2.since侧重主句,从句表示显然的或已为人所知的理由,常译为“因为”、“既然”,语气比because稍弱,通常置于句首,表示一种含有勉强语气的原因.例如：
(1)Since he asks you,you”ll tell him why.他既然问你,那就告诉他为什么吧.
(2)Since everyone is here,let”s start.既然大家都到齐了,我们就出发吧!
(3)Since I understood very little Japanese,I couldn”t follow the conversation.我日语懂得不多,因而听不懂对话
3.for后可接短语或名词
(1)We have studied English for years.
我们学英语已有好几年了.
(2)They jumped for joy.
他们高兴地跳了起来.
(3)Jim is going to get material for a new book.
吉姆正打算为一部新书准备材料.