as和because的作为引导原因状语时的区别,

常用的引导连词有because,as和since,三者的区别是：在回答问题的时候,使用because；对于显而易见的原因,常用as或since；as和since的从句常放在主句之前,而because的从句常放在主句之后.eg.
Why did you go? I went because Tom told me to go. 你为何去?那是因为汤姆叫我去.
He was angry not because we were late but because we made a noise.
他很生气不是因为我们来迟了,而是因为我们弄出了声音.
As it was raining hard,we had to be indoors. 由于雨太大,我们只好呆在家里.
Since you feel ill,you'd better not go to work. 既然你感觉不舒服,你最好不要去上班了.