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1、 when，while，as显然都可以引导时间状语从句，但用法区别非常大。一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as只能和延续性动词连用。Why do you want a new job when youve got such a good one already？（get为短暂性动词）你已经找到如此好的工作，为何还想再找新的？第1页/共11页 Why do you want a new job when youve got such a good one already？（get为短暂性动词）你已经找到如此好的工作，为何还想再找新的？The student
2、s took notes as they listened（listen为延续性动词）学生们边听课边做笔记。第2页/共11页 二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while和as从句的谓语动作必须是和主句谓语动作同时发生。第3页/共11页1从句动作在主句动作前发生，只用 when。When he had finished his homework，he took a short rest（finished先发生）当他完成作业后，他休息了一会儿。When I got to the airport，the guests had left（got to后发生）当我赶到飞
3、机场时，客人们已经离开了。第4页/共11页2从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。When While As we were dancing，a stranger came in（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。When While As she was making a phonecall，I was writing a letter（make为延续性动词）当她在打电话时，我正在写信。第5页/共11页3当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用 as。这时，as常
4、表示“随着”；“一边，一边”之意。As the time went on，the weather got worse（as表示“随着”之意）第6页/共11页 The atmosphere gets thinner and thinner as the height increases 随着高度的增加，大气越来越稀薄。As years go by，China is getting stronger and richer 随着时间一年一年过去，中国变得越来越富强了。The little girls sang as they went 小姑娘们一边走，一边唱。第7页/共11页4在将来时从句中，常用w
5、hen，且从句须用一般时代替将来时。When the manager comes here for a visit next week，Ill talk with him about this下周，经理来这参观时，我会和他谈谈此事。第8页/共11页三、when用于表示“一就”的句型中（指过去的事情）。sbhad hardly/scarcely done sthwhenHardly Scarcely had sbdone sthwhen 第9页/共11页我刚一闭上眼，就有人在敲门了。I had hardly scarcely closed my eyes when someone knocked at the doorHardly Scarcely had I closed my eyes when someone knocked at the door第10页/共11页感谢您的观看！第11页/共11页