1.引导原因状语从句的从属连词主要有because，as，since，seeing (that)， now (that)，not that … but that。如：
They can't have gone out because the light 's on.
Since you are going，I will go.既然你去，我也去。
Now that all are present，let's start the discussion.
Not that I don，t like the film，but that I have no time for it.
Since [As] we，ve no money，we can，t buy it.
Seeing that it's raining，we VI better stay indoors.
Now that you are here，you ’d better stay.
I can't tell you when you won't listen.
【正】 Because it was raining，we stayed at home. / It was raining，so we stayed at home.
【误】 Because it was raining，so we stayed at home.
4.because从句与because of短语的转换。because后跟句子，because of跟短语，二者可以转换。如：
He can't come because he is ill. / He can't come because of his illness.
I said nothing about it because his wife was there. / I said nothing about it because of his wife ’s being there.