my mother was watching TV ______my father came in.A when B a

my mother was watching TV ______my father came in.A when B as C because D while

A when
　　when 与 while 用法解析
　　连接词when与while是一对常与过去进行时合作的twins.但正如世界上没有两片完全相同的树叶一样,when与while在有着某些相似之处的同时,彼此也各有一些区别于对方的截然不同的“独特个性”.Do you want to know the differences between them?请看——
　　● when 解析版
　　〔引导时间状语从句〕具体地说,它有以下几种含义：
　　1．表明一个动作发生的时候,另一个动作正在进行之中.例如：
　　When the teacher came into the classroom ,we were reading English．当老师走进教室时,我们正在读英语.
　　2．表明当某一动作正在进行时,另一动作发生了.如：
　　When Kate was flying a kite,she found a wallet lying on the ground．凯特正在放风筝时,她发现地上有个钱包.
　　〔特别提示〕当when从句放在主句之后时,它更强调某一动作的突然性,此时的when相当于and then,and suddenly,just at that time.如；
　　1．We were watching TV when the telephone rang．（＝We were watching TV and suddenly the telephone rang．）我们正在看电视,（突然）电话铃响了.
　　试比较：When we were watching TV, the telephone rang．我们正在看电视时,电话铃响了.
　　2．The boys were playing football when it began to rain．男孩子们正在踢球时,（不料）开始下雨了.
　　3．I was taking a walk when I came across Lily．我正在散步时,（没想到）遇见了莉莉.
　　特别是主句中有just,或when从句中有suddenly时,这种突然性更为明显、强烈.例如：
　　4．He was just falling asleep when he heard someone shout,“Stop the thief!”他刚要入睡,突然听到有人喊：“抓贼!”
　　5．We were doing our homework at school last night when the lights went out．昨天晚上我们正在学校写作业时,灯（突然）灭了.
　　〔相关链接〕when引导的状语从句除了上述意义之外,也常具有其他一些含义：
　　1．一……就……（＝as soon as）
　　We will stand up when the teacher comesin．老师一进来我们就起立.
　　2．虽然；然而；可是（＝although）
　　We had only five boxes when we needed eight．我们需要八个箱子,可是只有五个.
　　3．每当……（＝whenever）
　　It is always very hot here when it is summer．每当夏季,这儿总是很热.
　　4．既然（＝since,as）
　　Why did you come here on foot when you know you should come by bike?既然你知道该骑自行车来,你为何还要步行呢?
　　● while 解析版
　　while引导状语从句,有以下两种含义：
　　1．表示某个动作正在进行的同时,另一动作也在进行之中,这时主从句都用进行时态,有对同类的两个动作进行对比的意味.如：
　　While I was playing the piano,she was dancing．我在弹钢琴,她在跳舞.
　　While Jim is picking apples,Kate is carrying apples to the truck．吉姆正在摘苹果,凯特正在把苹果搬到卡车上去.
　　2．表示某个动作正在进行时,又发生了另一动作（该动作用一般过去时）.如：
　　While I was reading,I fell asleep．我读着读着就睡着了.
　　While we were swimming in the river,we saw a fish jump out of the water．我们正在河中游泳时,看见一条鱼跃出了水面.
　　〔相关链接〕
　　while还有以下几种常见用法：
　　1．只要（＝as long as）
　　There will be life while there is water and air．只要有空气和水,就会有生命.
　　2．而；然而〔表示对比〕
　　He is a driver while I'm a teacher．他是司机,而我是老师.
　　3．虽然（＝although）；尽管〔表示让步〕
　　While I see what you say,I can't agree with you．虽然我能理解你说的话,但是我不能同意你.
　　4．用作名词,表示“一会儿或一段时间”,常与a,the或this等连用.如：
　　Just wait a while and then I will help you．等一下,我会来帮你的.
　　Where have you been all this while?这一阵子你一直都在哪儿?
　　● when 与 while 区别版
　　综上所述,我们可以看出when与while本质的区别在于：when既可以指某一点时间,也可以指某一段时间,其从句谓语动词表示的动作既可以是瞬间性的、非延续性的,也可以是延续性的；while指一段时间,从句中的谓语动词必须是延续性的.即：指一段时间时,when可用while来代替；指一点时间时,when不能用 while来代替.试比较：
　　When he woke up,it was eight o'clock．（√）
　　While he woke up,it was eight o'clock．（×）
　　When I was waiting for a bus,I met her．（√）
　　While I was waiting for a bus,I met her．（√）
　　●练习版 Can you say the following sentences in English?
　　1．当我们到达火车站时,天正下着雪.
　　______________________________
　　2．孩子们正在做游戏,突然铃响了.
　　______________________________
　　3．爸爸在洗车时,妈妈在做饭.
　　______________________________
　　4．琳达正在跑步时伤了自己的左腿.
　　______________________________
　　5．我们在西安时,每天见面.
　　______________________________
　　Key:
　　1．When we got to the train station,it was snowing．
　　2．The children were playing games when the bell rang．
　　3．While dad was washing his car,mum was cooking．
　　4．When ／While Linda was running,she hurt her left leg．
　　5．When ／While we were in Xi'an,we met every day． when和while引导的时间状语从句与这一时态连用.所以区别when和while的用法成了这一单元的难点. （一）、when,while都有“当……时候”的意思.when既可表示某一点时间,也可以表示某一段时间 .在when引导的时间状语从句中,其谓语动词可以是延续性的,也可以是非延续性的,可与主句中的谓语动词同时发生,也可在其后发生. 例如： 1、I was just reading a book when she came into my room. 她走进我房间时,我正在看书. 2、Were you writing when the teacher came in? 老师进来的时候,你在写信吗? 3、When he was a child he was always trying out new ideas. 他小时候就常常试验一些新的设想. （二）、while只能表示某一段时间,不能表示某一点时间.在while引导的时间状语从句中,其谓语动词只能是延续性的,而且也只能与主句中的谓语动词同时发生或存在. 例如： 1、While Jim was mending his bike, Lin Tao came to see him. 正当吉姆修自行车时,林涛来看他. 2、You can’t do your homework while you’re watching TV. 你不能一边看电视一边做家庭作业. （三）、另外,when和while的区别还在于：while引导的时间状语从句多用进行时态,而when引导的时间状语从句多用一般时态. 例如： 1、While they were talking , the bell rang. 正在他们谈话的时候,上课铃响了. 2、I was doing my homework when my mother came back home yesterday evening. 昨天晚上妈妈回家的时候,我正在做家庭作业