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专题六 状语从句 ◆时间状语从句的考查要点 1．before引导的从句中不用否定式谓语。常用如下句型： It will be long before...(得过好久才……) It will not be long before...(过不了多久就……) It was long before... (过了好久才……) It was not long before... (过了不久就……) 2．since后面所用动词不同，该动词所表示动作持续时间的计算方法也不同。 It is two years since he joined the army.他参军两年了。 It is two years since he smoked.他戒烟两年了。 3．as，when，while用法一览表。 类别 作用 例句as 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.(同时) The runners started as the gun went off.(几乎同时) when (at or during the time that )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.(指时间点) When we were at school，we went to the library every day.(在一段时间内) while 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 don’t talk so loud while others are working. | 
