(1)原因状语从句通常由because, since, as引导。例如:
①He didn’t come to school because he was ill.
②As it is raining, we shall not (不得;不应该)go the zoo.
③Since you can’t answer the question, I’ll ask someone else.
(2)because表示直接原因,语气最强。Because引导的原因状语从句多放在主句之后。回答由why提出的问题,只能用because。As和since语气较弱,一般用来表示明显的原因。由as和since引导的原因状语从居多放在句首。例如:
①--Why aren’t going there?
--Because I don’t want to.
②As he has no car, he can’t get there easily.
③Since we have no money, we can’t buy it.
(3)because和so不能同用在一个句子里。
