备战职称英语考试：重点语法解析(5)

　　状语从句指句子用作状语时,起副词作用的句子.它可以修饰谓语、非谓语动词、定语、状语或整个句子.

　　根据其作用可分为时间、地点、原因、条件、目的、结果、让步、方式和比较等从句.状语从句一般由连词引导,也可以由词组引起.从句位于句首或句中时通常用逗号与主句隔开,位于句尾时可以不用逗号隔开.

　　考点聚焦

　　1、时间状语从句

　　as、when、while用

　　as表示当的时候,往往和when/ while通用,但它着重强调主句与从句的动作或事情同时或几乎同时发生.

　　She came up as I was cooking.

　　The runners started as the gun went off.

　　when:既可以表示在某一点的时候,又可表示在某一段时间内,主句与从句的动作或事情可以同时发生也可以先后发生.

　　It was raining when we arrived.

　　When we were at school, we went to the library every day.

　　while意思是当的时候或在某一段时间里.主句中的动作或事情在从句中的动作或事情的

　　进展过程中发生,从句中的动词一般要用延续性动词.在when表示a period of time时,两者可以互换.

　　Please dont talk so loud while others are working.

　　He fell asleep while/when reading. Strike while the iron is hot.

　　引导时间状语从句的连接词除上述外还有:

　　①till, not until , until, before, since

　　Dont get off the bus until it has stopped.

　　He waited for his father untilit was twelve oclock.

　　It will be five years before he returns from England