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连词用来连接词，短语，从句或句子。连词在句中(能/不能)单独使用。连词可分为两类：并列连词和从属连词。

1)      并列连词

※表并列关系：and, both… and/not only… but (also)/as well, neither.. nor

※表转折关系：but, yet, however, still, while

※表选择关系：or, either… or        ※表因果关系：for, so, therefore

2)      从属连词用来引导从句

※表时间：as/ when/while, before/after, till/until, since, as soon as

※表地点：where(ever)              ※表条件：if/unless(除非)

※表原因：because/as/since/now that   ！because与so不能连用

※表比较：than, as…as…/not as(so)…as/

※表让步：(al)though/even if(though)   ! although与but不能连用

※表目的：so that/ in order that       ※表结果：so/such… that…

※表方式：as/as if (though)             ※引导名词从句：that, if, whether

3)      常用连词的用法辨析

※ While, When, As三个连词都可引导时间状语从句如：As/When/While I was walking down the street I noticed a police car.（表示某事进行中，又发生了另一事）但各词用法有所不同。①While常用表同时进行的两个长动作。如：While mother was cooking lunch, I _________ (do) my homework. ②When常用表示两动作先后发生。如：When(after) he (had) finished his work, he took a short rest. ③当从句是瞬间动词，主句是延续动词时，从句用when。如：When John arrived, I ______(cook) lunch. ④As常用来表示发展变化的两个动作。如：As the days get longer in the day, the nights get shorter in summer. ⑤As还可用来表示同时发生的两个短动作。如：She looked behind from time to time as she rode her bike home.

※As, Because, Since , For这四个词都可表原因，但用法有区别。①Because引导的从句往往放在句___，表直接原因。如：I stayed at home because it rained. ②As和Since 引导的从句一般放在句___，表原因已被人们所知。如：Since everybody is here, let’s begin. ③for用来补充说明理由，____(可/不可)放在句首。如：The spring comes, for the grass is green.

※if, whether  都可作“是否”讲，引导宾与从句时可互换。下列情况下，不能用if，只能用whether ①引导__语从句Whether he will come to the party is unknown. ②引导____语从句The question is whether I can pass the exam.③在___前。I haven’t made up my mind whether to go there or not.

※either…or…, neither…nor, not only…but also…这三个连词词组连接两个并列主语时，谓语动词要随相邻的主语变化。例如：Either you or he____ (be) wrong. Neither Mr. Black nor his children ______ (enjoy) fish. Not only the teacher but also the students ____________ (be) to Shanghai World Expo already.