从属连词
从属连词通常引导一个从句修饰主句一般可分为引导名词性从句（宾语从句或表语从句等）和引导状语从句的从属连词
(1) 引导名词性从句的从属连词主要有that，if（是否），Whether（是否）等I don"t know if he"II come today．我不知道他是否会来。（引导宾语从句）The problem is that we haven"t got enough money.问题是我们没有足够的钱。（引导表语从句）
(2)引导状语从句的从属连词有很多时间状语从句when，while，as，after，beforeuntil，till , as soon asThey had left when I got there.当我到那里时他们已经离开了。地点状语从句wherewhereverWhere there is a will, there is a way．有志者，事竞成。原因状语从句becausesinceas（因为）now thatI drove slowly because there was such heavy traffic.我开得很慢，因为车太多了。条件状语从句if ( 如果 )unlessonce（一旦）in caseWe"ll go fishing if it doesn"t rain tomorrow．如果明天不下雨，我们就去钓鱼。目的状语从句in order thatso thatI got up early so thatI could catch the first bus.我起得很早，为的是赶上第一趟车。让步状语从句although / thougheven if / thoughhoweverThough Canada is large, the population is small。尽管加拿大面积大，人口却很少。结果状语从句so…thatso thatsuch…that…He was so tired that he fell asleep fast.他累得很快就睡着了。比较状语从句thanas / so…as…less / more…I"m older than you.我年龄比你大。方式状语从句as（按照）if / though（好像）You should do as l told you．你应该按我说的做。
不能同时出现在一个句子中的连词
1、besause（因为）, so（所以）不能同时出现在一个句子里只能用其一Because he was tired, he couldn"t walk there.=He was tired, so he couldn"t walk there.因为他累了，所以他不能走到那儿了。
2、(al)though（虽然）, but（但是）不能同时出现在一个句子里只能用其一但 though 和 yet 可以同时出现在一个句子里（yet用作副词）Though he was tired, he still worked hard.=He was tired, but he still worked hard.虽然他很累，但他仍然努力工作。
