while这个词在什么时候用?

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while这个词在什么时候用?

While的用法
一、while用作名词时,意为“一段时间,一会儿”.例如:
  I stayed there for a short while.(我在那儿呆了一小会儿.)
  The postman came a short while ago.(邮递员刚刚来过.)
  二、while用作连词时,有以下几种含义:
  1、意为“当……时候,和……同时”,引导时间状语从句.例如:
  While I was watching TV,the bell rang.我看电视时,铃响了.)
  Tom watched TV while she ate her supper.(汤姆边吃晚饭边看电视.)
  2、意为“虽然,尽管”,引导让步状语从句.例如:
  While it was late,he went on working.(虽然很晚了,但他还在继续工作.)
  While he is in poor health,he works hard.(虽然他身体不好,但他还是努力工作.)
  3、连接两个并列句子,表示“对比”关系.例如:
  He went out for a walk,while I stayed at home.(他出去散步了,而我却呆在家里.)
  I like singing while she likes dancing.(我喜欢唱歌,而她喜欢跳舞.)
  You like sports,while I prefer music.(你喜欢体育,而我更喜欢音乐.)
  三、while引导状语从句时,应注意以下几点:
  1、while引导的时间状语从句既可放在句首,也可放在句末;而while引导的让步状语从句一般放在句首,不放在句末.另外,也可以从意义上加以区分.例如:
  While he was tired,he went on working.(虽然他累了,但他还是继续工作.)
  (while引导让步状语从句)
  While he was tired,he would have a rest.(他累了就休息一会儿.)
  (while引导时间状语从句)
  2、while引导让步状语从句时,如果从句的主语和主句的主语相同,那么从句的主语和谓语动词be都可以省略.例如:
  While he was ill,he went there.(=While ill,he went there.)
(虽然他有病,但他还是去那里了.)
  3、while和when都可以引导时间状语从句,但应注意:while引导的时间状语从句中的谓语动词必须是延续性的动词;而when引导的时间状语从句中的谓语动词既可以是延续性动词,也可以是非延续性动词.当时间状语从句中的谓语动词是延续性动词时,while和when可以互相替换.例如:
  While we were talking,the teacher came in.(我们正在谈话时,老师进来了.)
  The bus had left when we arrived at the bus stop.(当我们到达车站时,公共汽车已经开走了.)
  (arrive是非延续性动词,因此,此句中的when不能用while替换.)
  When/While we were having a meeting,our teacher came in.(我们正在开会时,老师走了进来.)
  (have是延续性动词,因此,句中的when可以用while替换.)
  4、while引导的状语从句还可以表示“某个动作正在进行的同时,另一个动作也在进行之中”.例如:
  While the teacher was speaking,the students were listening.(老师讲课时,学生们在听.)
  While he was writing,I was reading.(他写字时,我在看书.)