連詞有：because as since now that等

　　(1) 區(qū)分because, as, since, for

　　① because表示人們不知道的直接的原因或理由，著重點在從句，其所引導(dǎo)的從句，為全句句意的中心所在。通常用于回答why引出的疑問句，語氣最強，除特別強調(diào)外，該從句一般位于主句后面，不能與so連用但是可以與so進(jìn)行同義句轉(zhuǎn)換。

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

　　我沒有和她一起出國是因為費用太高。

　�、� as引導(dǎo)的原因狀語從句所傳遞的通常是已知信息，從句多位于主句之前，表示雙方那個已知的理由，如：

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

　　我不認(rèn)識路，因而問警察。

　�、� since引導(dǎo)的原因狀語從句多表示大家眾所周知的理由，如：

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

　　既然乘飛機旅行快得多，他們就決定坐飛機。

　　④ for表示的理由是附加的或推斷的，并非此原因，通常與主句用逗號隔開，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引導(dǎo)的原因狀語從句

　　Now that "因為;既然"，通常可以和since換用。用來表示一種新的情況，再加以推論。如：

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

　　你既已考試合格，就可以獨自開車了。