连词有：because as since now that等

　　(1) 区分because, as, since, for

　　① because表示人们不知道的直接的原因或理由，着重点在从句，其所引导的从句，为全句句意的中心所在。通常用于回答why引出的疑问句，语气最强，除特别强调外，该从句一般位于主句后面，不能与so连用但是可以与so进行同义句转换。

　　I didn't go aboard with her because I couldn't afford it.

　　我没有和她一起出国是因为费用太高。

　　② as引导的原因状语从句所传递的通常是已知信息，从句多位于主句之前，表示双方那个已知的理由，如：

　　As I didn't know the way，I asked a policeman.

　　我不认识路，因而问警察。

　　③ since引导的原因状语从句多表示大家众所周知的理由，如：

　　Since traveling by air is much faster, they decided to take a plane.

　　既然乘飞机旅行快得多，他们就决定坐飞机。

　　④ for表示的理由是附加的或推断的，并非此原因，通常与主句用逗号隔开，不位于句首，如：

　　He must be not at home, for the telephone isn't answered.

　　用because, as, since, for 填空：

　　We'll have to go to bed early ___________ we'll start off early tomorrow.

　　___________ you know all about it, tell me please.

　　____________ all the seats were taken, I had to stand.

　　He must be at work, __________ the light in his office is still on.

　　Lily didn't go to school ___________ she was ill.

　　=_________________________________________________________.

　　(4) now that引导的原因状语从句

　　Now that "因为;既然"，通常可以和since换用。用来表示一种新的情况，再加以推论。如：

　　Now(that) you have passed your test, you can drive on your own.

　　你既已考试合格，就可以独自开车了。