求.when,while,as的练习题,各两题.（最好能表明答案和为什么）谢谢.

求.when,while,as的练习题,各两题.（最好能表明答案和为什么）谢谢.
求.when,while,as的练习题,各两题.（最好能表明答案和为什么）谢谢.

求.when,while,as的练习题,各两题.（最好能表明答案和为什么）谢谢.
这三个连词都可作"当……的时候"解,但它们之间有一些细微的差别.
1.when(at or during the time that)只表示一般的时间关系,它既可指时间的一点(a point of time),也可指一段时间(a period of time).用when时,从句的动作可与主句的动作同时发生,也可先于主句的动作,因此when用得最多.如：
When the clock struck twelve,all the lights went out.当时钟敲了十二下,灯全部都熄了.
He raised his hat when he saw her.当他看见她的时候,频频举帽示敬.
When two bodies are rubbed together,heat is produced.当两个物体摩擦时就会产生热.
Don't forget to return this book for me,when you go to the library.你去图书馆时,不要忘记替我还这本书.
2.while(during the time that)只能指一段时间,而不能指时间的一点.用while时,从句的动作或者与主句的动作同时发生,或者主句的动作是在从句的动作的进展过程中发生的.因此,从句中的谓语必须是表示延续性动作或状态的动词.这是while与when的主要差别.如：
Strike while the iron is hot.趁热打铁.
When we arrived in Beijing,it was raining.(arrive不是延续性的动词)我们到达北京时,天正在下雨.
Please don't talk so loud while people are working.别人在工作的时候,请不要大声讲话.
在用when和while连接的从句中,常省略与主句相同的主语和相应的be,而在as连接的从句中一般则不省略.如：
Wood gives much smoke while(it is)burning.木头燃烧时冒出许多烟.
He fell asleep while(he was)studying his grammar book.他在阅读语法书的时候睡着了.
While in London,he studied music.他在伦敦的时候,研究音乐.
When(they are)heated,metals expand.金属受热时膨胀.
when和while还可作并列连词用：when作"那时"解,前面有逗号,不能用while代替；while表示对比,作"而"解,前面常有逗号.
The Queen will visit the town in May,when she will open the new hospital.女王将于五月访问该城,届时她将主持一所新医院的开幕式.
Soon the water in the flask will boil,when you may pour some cold water over it.烧瓶中的水一会儿就要开了,那时你可把凉水浇在烧瓶上.
Some materials are weldable,while others are not.一些材料是可焊的,而另一些则是不可焊的.
The enemy rots with every passing day,while for us things are getting better daily.
敌人一天天烂下去,我们一天天好起来.
3as(at the same moment that)往往可与when通用,但它着重指从句与主句的动作相伴随发生,可译成："一面……一面","随着……".as用得较多.如：
Kate read the book as she went along.凯特边走边读书.
As the car moved faster and faster,it gained more and more kinetic energy.当汽车行驶得越来越快时,它得到的动能也越来越多.
We took notes as we listened to the lecture.我们边听课边记笔记.
As it became more common for women to work outside the house,men began to share the housework.随着妇女就业普遍了,男职工分担了家务劳动.