Exercise of when, while
一.用when或while填空
1. _____ the teacher came in, we were talking.
_____ we were talking, the teacher came in.
2. He was driving along ____ suddenly a woman appeared.
3. ____ Jack was waiting at the door, an old woman called to
him.
4. He was reading a book ____ suddenly the telephone rang.
5. ____ it began to rain, they were playing chess.
6. She saw a taxi coming ____ the woman was waiting under
the streetlight.
7. While Jack _________(look) for customers, he _______(see)
an old man.
8. John __________(sleep) when someone_____(steal) his car.
9. He is strong_____ his brother is weak.
10. The children were running to move the bag of rice ______
they heard the sound of a motor bike.
Exercise of noun.
一.选择填空
1. There are living a few______ at the foot of the hill.
A. families
B. family
C. people
D. person
2. --How did you enjoy the concert last night?
--______
A. What a disappointment!
B. What a failure!
C. Awful!
D. Very dissatisfactory!
3. The shoes ___ mine, but that pair of shoes ___ my brother’s.
A. is, is
B. is, are
C. are, are
D. are, is
4. They got much _____ from those new books.
A. ideas
B. photos
C. news
D. stories
5. I have two _______ and three bottles of _________ here.
A. orange, orange
B. oranges, oranges
C. oranges, orange
D. orange, oranges
6. Every evening M r. King takes a _________ to his home.
A. 25 minutes’ walk
B. 25 minute’s walk
C. 25 minute walk
D. 25 minutes walk
7. An old _______ wants to see you.
A. people
B. person
C. the people
D. the person
8. ________ mothers couldn’t go to the meeting, because they have gone to Shanghai .
A. Mary and Peter’s
B. Mary and Peter
C. Mary’s and Peter
D. Mary’s and Peter’s
9. Li Lei has been to __________ many times this month.
A. her uncle
B. her uncle’s
C. her uncles
D. aunt’s
10. He is a success as a leader but he hasn’t ________ in teaching.
A. many experiences
B. much experience
C. an experience
D. a lot experience
11. A classmate of _________ was here ten minutes ago.
A. you
B. your
C. your sister
D. your sister’s
12. A group of _________ are talking with two ___________.
A. Frenchmen, Germans
B. Germans , Frenchmans
C. Frenchmans , Germen
D. Germen , Frenchmen
13. The team ________ having a meeting.
A. is
B. are
C. am
D. be
14. “Would you like _________?”“________,please.”
A. drink, Three coffees
B. a cup of drink, Coffees
C. a drink, a coffee
D. a drink, Three cups of coffees
15. The Great Wall was made not only by _______, but also the flesh and blood of ________ men.
A. earth and stone, millions of
B. earths and stones, millions
C. the earth and stone, million of
D. the earths and stones, millions
16. Help yourself to __________.
A. chickens and apples
B. chickens and apple
C. chicken and apple
D. chicken and apples
17. Oh, dear. I forgot the two _________.
A. room’s number
B. rooms’ number
C. room numbers
D. rooms’ numbers
18. She has been in Tianjin for ten years. Tianjin has become her second _________.
A. family
B. house
C. home
D. room
19. Excuse me, how can I get to the nearest ___ shop?
A. shoes
B. shoe
C. shoes’
D. shoes
20. You need more ___ to keep fit.
A. practice
B. train
C. exercises
D. exercise
when 和while的用法区别 两者的区别如下： ①when是at or during the time that, 既指时间点，也可指一段时间； while是during the time that，只指一段时间，因此when引导的时间状语从句中的动词可以是终止性动词，也可以是延续性动词，而while从句中的动词必须是延续性动词。 ②when 说明从句的动作和主句的动作可以是同时，也可以是先后发生；while 则强调主句的动作在从句动作的发生的过程中或主从句两个动作同时发生。 ③由when引导的时间状语从句，主句用过去进行时，从句应用一般过去时；如果从句和主句的动作同时发生，两句都用过去进行时的时候，多用while引导，如： a. When the teacher came in, we were talking. 当此句改变主从句的位置时，则为： While we were talking, the teacher came in. b. They were singing while we were dancing. ④when和while 还可作并列连词。when表示“在那时”；while表示“而，却”，表对照关系。如： a. The children were running to move the bag of rice when they heard the sound of a motor bike. 孩子们正要跑过去搬开那袋米，这时他们听到了摩托车的声音。 b. He is strong while his brother is weak. 他长得很结实，而他弟弟却很瘦弱。 一。引导时间状语从句时，WHILE连接的是时间段，而WHEN连接的多是时间点 例如What does your father do while your mother is cooking? What does your mother do when you come back? 二，WHILE可以连接两个并列的句子，而WHEN不可以 例如I was trying my best to finish my work while my sister was whtching TV 三，WHEN是特殊疑问词，对时间进行提问，WHILE不是。 例如，When were you bron? 续性动词和短暂性动词 英语中的动词，是学习中的重点，又是难点。英语中的动词有多种分类法。根据其有无含义，动词可分为实义动词和助动词；根据动词所表示的是动作还是状态，可以分为行为动词和状态动词；根据动词所表示的动作能否延缓，分为延续性动词和终止性动词。 可以表示持续的行为或状态的动词，叫做“延续性动词”，也叫“持续性动词”，如：be, keep, have, like, study, live, etc. 有的表示短暂、瞬间性的动词，叫做“终止性动词”，也可叫“短暂性动词”，或“瞬间性动词”，如die, join, leave, become, return, reach, etc.
when和while用法区别专项练习 讲解三例句： 1. The girls are dancing while the boys are singing. 2. Kangkang’s mother is cooking when he gets home. 3. When/While Kangkang’s mother is cooking, he gets home. 一、用when或者while填空 Margo was talking on the phone, her sister walked in. we visited the school, the children were playing games. · Sarah was at the barber’s, I was going to class. I saw Carlos, he was wearing a green shirt. Allen was cleaning his room, the phone rang. Rita bought her new dog; it was wearing a little coat. 7. He was driving along ________ suddenly a woman appeared. 8. _____ Jake was waiting at the door, an old woman called to him. 9. He was reading a book ______suddenly the telephone rang. 10. ______ it began to rain, they were playing chess. [ 二、用所给动词适当形式填空 11. While Jake __________ (look) for customers, he _______ (see) a woman. 12. They __________ (play) football on the playground when it _____ (begin) to rain. 13. A strange box ________ (arrive) while we _________ (talk). 14. John ____________ (sleep) when someone __________ (steal) his car. 15. Father still (sleep) when I (get) up yesterday morning. 16. Grandma (cook) breakfast while I (wash) my face this morning. 17. Mother (sweep) the floor when I (leave) home. ~ 18. I (read) a history book when someone (knock ) at the door. 19. Mary and Alice are busy (do) their homework. 20. The teacher asked us (keep) the windows closed. 21. I followed it (see) where it was going. 22. The students (play) basketball on the playground from 3 to 4 yesterday afternoon. / 三、完成下面句子，词数不限 1.飞机在伦敦起飞时正在下雨。 It when the plane in London. 2.你记得汶川大地震时你在做什么吗 Do you remember what you when Wenchuan Earthquake . 3.当铃声想起的时候，我们正在操场上玩得很开心。 We on the playground when the bell . 4.当妈妈下班回家时，你在做什么 % when Mum from work 5.当我在做作业时，有人敲门。 I was doing my homework, someone
1.______ Margo was talking on the phone,her sister walked in. 2.______ we visited the school,the children were playing games. 3.______ Sarah was at the barber's,I was going to class. 4.______ I saw Carlos,he was wearing a green shirt. 5.______ Allen was cleaning his room,the phone rang. 6.______ Rita bought her new dog,it was wearing a little coat. 7.He was driving along ________ suddenly a woman appeared. 8. _____ Jake was waiting at the door, an old woman called to him 9.He was reading a book ______suddenly the telephone rang. 10. ______ it began to rain, they were playing chess. 11. She saw a taxi coming ______ the woman was waiting under the streetlight. 12. the allien was in the museum,I called the police. 13.The boy was walking down the street a UFO landed. 14. the alien was visiting the museum,the boy called the TV station. 15.I was cleaning my room the fire broke out. 16. Linda shouted his name,some people looked at her. 用所给动词适当形式填空 17.While Jake __________(look) for customers, he _______(see) a woman. 18. They ____________(play) football on the playground when it ______(begin) to rain.
when和while的用法解析、练习题及答案（附总结表格） 一、讲解三例句: 1. The girls are dancing while the boys are singing. 2. Lucy’s mother is cooking when she gets home. 3. When/While Lucy’s mother is cooking, she gets home. 二、用when或者while填空 1.______ Margo was talking on the phone, her sister walked in. 2.______ we visited the school, the children were playing games. 3.______ Sarah was at the barber’s, I was going to class. 4.______ I saw Carlos, he was wearing a green shirt. 5.______ Allen was cleaning his room, the phone rang. 6.______ Rita bought her new dog; it was wearing a little coat. 7. He was driving along ________ suddenly a woman appeared. 8. _____ Jake was waiting at the door, an old woman called to him. 9. ______ it began to rain, they were playing chess. 10. She saw a taxi coming ______ the woman was waiting under the streetlight. 三、语法 while和when都是表示同时，到底句子中是用when还是while主要看主句和 从句中所使用 的动词是短暂性动作(瞬时动词)还是持续性动作。 1、若主句表示一个短暂性动作，而从句表示的是一个持续性动作时，用 When/While。如: He fell asleep when while he was reading. 他看书时睡着了。
第二章线性表 2.1 填空题 (1)一半插入或删除的位置 (2)静态动态 (3)一定不一定 (4)头指针头结点的next 前一个元素的next 2.2 选择题 (1)A (2) DA GKHDA EL IAF IFA(IDA) (3)D (4)D (5) D 2.3 头指针：在带头结点的链表中，头指针存储头结点的地址；在不带头结点的链表中，头指针存放第一个元素结点的地址； 头结点：为了操作方便，在第一个元素结点前申请一个结点，其指针域存放第一个元素结点的地址，数据域可以什么都不放； 首元素结点：第一个元素的结点。 2.4已知顺序表L递增有序，写一算法，将X插入到线性表的适当位置上，以保持线性表的有序性。 void InserList(SeqList *L,ElemType x) { int i=L->last; if(L->last>=MAXSIZE-1) return FALSE; //顺序表已满 while(i>=0 && L->elem[i]>x) { L->elem[i+1]=L->elem[i]; i--; } L->elem[i+1]=x; L->last++; } 2.5 删除顺序表中从i开始的k个元素 int DelList(SeqList *L,int i,int k) { int j,l; if(i<=0||i>L->last) {printf("The Initial Position is Error!"); return 0;} if(k<=0) return 1; /*No Need to Delete*/ if(i+k-2>=L->last) L->last=L->last-k; /*modify the length*/
WHEN与WHILE用法区别 when, while这三个词都有"当……时候"之意，但用法有所不同，使用时要特别注意。 ①when意为"在……时刻或时期"，它可兼指"时间点"与"时间段"，所引导的从句的动词既可以是终止性动词，也可是持续性动词。如： When I got home, he was having supper.我到家时，他正在吃饭。 When I was young, I liked dancing.我年轻时喜欢跳舞。 ②while只指"时间段"，不指"时间点"，从句的动词只限于持续性动词。如：While I slept, a thief broke in.在我睡觉时,盗贼闯了进来。 辨析 ①when从句与主句动作先后发生时，不能与while互换。如： When he has finished his work, he takes a short rest.每当他做完工作后，总要稍稍休息一下。(when = after) When I got to the cinema, the film had already begun.当我到电影院时，电影已经开始了。(when=before) ②when从句动词为终止性动词时，不能由while替换。如： When he came yesterday, we were playing basketball.昨天他来时，我们正在打篮球。 ③当从句的谓语是表动作的延续性动词时，when, while才有可能互相替代。如：While / When we were still laughing, the teacher came in.正当我们仍在大声嬉笑时，老师进来了。 ④当从句的谓语动词是终止性动词，而且主句的谓语动词也是终止性动词 时,when可和as通用，而且用as比用when在时间上更为紧凑，有"正当这时"的含义。如： He came just as (or when) I reached the door.我刚到门那儿，他就来了。 ⑤从句的谓语动词如表示状态时，通常用while。如： We must strike while the iron is hot.我们应该趁热打铁。 ⑥while和when都可以用作并列连词。
as when while 的区别和用法 as when while的用法 一、as的意思是“正当……时候”,它既可表示一个具体的时间点，也可以表示一段时间。as可表示主句和从句的动作同时发生或同时持续，即“点点重合”“线线重合”；又可表示一个动作发生在另一个动作的持续过程中，即“点线重合”， 但不能表示两个动作一前一后发生。如果主句和从句的谓语动词都表示持续性的动作，二者均可用进行时，也可以一个用进行时，一个用一般时或者都用一般时。 1、As I got on the bus，he got off. 我上车，他下车。（点点重合）两个动作都是非延续性的 2、He was writing as I was reading. 我看书时，他在写字。（线线重合）两个动作都是延续性的 3、The students were talking as the teacher came in. 老师进来时，学生们正在讲话。（点线重合）前一个动作是延续性的，而后一个动作时非延续性的 二、while的意思是“在……同时（at the same time that )”“在……期间(for as long as, during the time that）”。从while的本身词义来看，它只能表示一段时间，不能表示具体的时间点。在时间上可以是“线线重合”或“点线重合”，但不能表示“点点重合”。例如： 1、He was watching TV while she was cooking. 她做饭时，他在看电视。（线线重合） 2、He was waiting for me while I was working. 我工作的时候，他正等着我。（线线重合） 3、He asked me a question while I was speaking. 我在讲话时，他问了我一个问题。（点线重合）
精品文档 精品文档when和while用法区别专项练习 讲解三例句： 1. The girls are dancing while the boys are singing. 2. Kangkang’s mother is cooking when he gets home. 3. When/While Kangkang’s mother is cooking, he gets home. 一、用when或者while填空 1.______ Margo was talking on the phone, her sister walked in. 2.______ we visited the school, the children were playing games. 3.______ Sarah was at the barber’s, I was going to class. 4.______ I saw Carlos, he was wearing a green shirt. 5.______ Allen was cleaning his room, the phone rang. 6.______ Rita bought her new dog; it was wearing a little coat. 7. He was driving along ________ suddenly a woman appeared. 8. _____ Jake was waiting at the door, an old woman called to him. 9. He was reading a book ______suddenly the telephone rang. 10. ______ it began to rain, they were playing chess. 二、用所给动词适当形式填空 11. While Jake __________ (look) for customers, he _______ (see) a woman. 12. They __________ (play) football on the playground when it _____ (begin) to rain. 13. A strange box ________ (arrive) while we _________ (talk). 14. John ____________ (sleep) when someone __________ (steal) his car. 15. Father still (sleep) when I (get) up yesterday morning. 16. Grandma (cook) breakfast while I (wash) my face this morning. 17. Mother (sweep) the floor when I (leave) home. 18. I (read) a history book when someone (knock) at the door. 19. Mary and Alice are busy (do) their homework. 20. The teacher asked us (keep) the windows closed. 21. I followed it (see) where it was going. 22. The students (play) basketball on the playground from 3 to 4 yesterday afternoon. 三、完成下面句子，词数不限 1.飞机在伦敦起飞时正在下雨。 It when the plane in London. 2.你记得汶川大地震时你在做什么吗？ Do you remember what you when Wenchuan Earthquake . 3.当铃声想起的时候，我们正在操场上玩得很开心。 We on the playground when the bell . 4.当妈妈下班回家时，你在做什么？ when Mum from work? 5.当我在做作业时，有人敲门。 I was doing my homework, someone the door. 6.当外星人正在买纪念品的时候，那个女孩报了警。 the alien was buying the souvenirs, the girl the police. 答案： 1.while 2.when 3.while 4.when 5.while 6.when 7.When 8.While 9.When 10.When 11.was looking ,saw 12.were playing,began 13.arrived, were talking 14.was sleeping, stole15..was,sleeping got 16.was cooking, was washing 17.was sweeping,left 18,was reading,knocked
过去进行时过去进行时表示过去某一时刻或者某段时间正在进行或发生的动作，常和表过去的时间状语连用，如： 1. I was doing my homework at this time yesterday. 昨天的这个时候我正在做作业。 2. They were waiting for you yesterday. 他们昨天一直在等你。 3. He was cooking in the kitchen at 12 o'clock yesterday. 昨天12点，他正在厨房烧饭。 过去进行时的构成： 肯定形式：主语+was/were+V-ing 否定形式：主语+was not (wasn't)/were not (weren't)+V-ing 疑问形式：Was/Were+主语+V-ing。 基本用法： 1. 过去进行时表示过去某一段时间或某一时刻正在进行的动作。常与之连用的时间状语有，at that time/moment, (at) this time yesterday (last night/Sunday/week…), at+点钟+yesterday (last night / Sunday…)，when sb. did sth.等时间状语从句，如： 1）What were you doing at 7p.m. yesterday? 昨天晚上七点你在干什么？ 2）I first met Mary three years ago. She was working at a radio shop at the time. 我第一次遇到玛丽是在三年前，当时她在一家无线电商店工作。 3）I was cooking when she knocked at the door. 她敲门时我正在做饭。 2. when后通常用表示暂短性动词，while后通常用表示持续性动词，而while所引导的状语从句中，谓语动词常用进行时态，如： When the car exploded I was walking past it. = While I was walking past the car it exploded. 3. when用作并列连词时，主句常用进行时态，从句则用一般过去时，表示主句动作发生的过程中，另一个意想不到的动作发生了。如： I was walking in the street when someone called me. 我正在街上走时突然有人喊我。 4. when作并列连词，表示“（这时）突然”之意时，第一个并列分句用过去进行时，when引导的并列分句用一般过去时。如：
用when或者while填空 1.______ Margo was talking on the phone,her sister walked in. 2.______ we visited the school,the children were playing games. 3.______ Sarah was at the barber's,I was going to class. 4.______ I saw Carlos,he was wearing a green shirt. 5.______ Allen was cleaning his room,the phone rang. 6.______ Rita bought her new dog,it was wearing a little coat. 7.He was driving along ________ suddenly a woman appeared. 8. _____ Jake was waiting at the door, an old woman called to him. 9.He was reading a book ______suddenly the telephone rang. 10. ______ it began to rain, they were playing chess. 11. She saw a taxi coming ______ the woman was waiting under the streetlight. 12. the allien was in the museum,I called the police. 13.The boy was walking down the street a UFO landed. 14. the alien was visiting the museum,the boy called the TV station. 15.I was cleaning my room the fire broke out. 16. Linda shouted his name,some people looked at her. 用所给动词适当形式填空 17.While Jake __________(look) for customers, he _______(see) a woman. 18. They ____________(play) football on the playground when it ______(begin) to rain. 19.A strange box ________(arrive) while we _________ (talk). 20. John ____________(sleep) when someone __________(steal) his car. 21.Father still (sleep)when I (get)up yesterday morning. 22.Grandma (cook) breakfast while I (wash) my face this morning. 23.Mother (sweep)the floor when I (leave)home. 24.I (read) a history book when someone (knock) at the door. 25.Mary and Alice are busy (do)their homework. 26.The teacher asked us (keep) the windows closed. 27.I followed it (see)where it was going. 28.The students (play)basketball on the playground from 3 to 4 yesterday afernoon.. 完成下面句子，词数不限 1.飞机在伦敦起飞时正在下雨。 It when the plane in London. 2.你记得汶川大地震时你在做什么吗？ Do you what you when Wenchuan Earthquake . 3.当铃声想起的时候，我们正在操场上玩得很开心。 We on the playground when the bell . 4.当妈妈下班回家时，你在做什么？ Mum from work? 5.当我在做作业时，有人敲门。 ，someone the door. 6.当外星人正在买纪念品的时候，那个女孩报了警。
第2章人工智能与知识工程初步 1. 设有如下语句，请用相应的谓词公式分别把他们表示出来：s (1)有的人喜欢梅花，有的人喜欢菊花，有的人既喜欢梅花又喜欢菊花。 解：定义谓词d P(x)：x是人 L(x,y)：x喜欢y 其中，y的个体域是{梅花，菊花}。 将知识用谓词表示为： (?x )(P(x)→L(x, 梅花)∨L(x, 菊花)∨L(x, 梅花)∧L(x, 菊花)) (2) 有人每天下午都去打篮球。 解：定义谓词 P(x)：x是人 B(x)：x打篮球 A(y)：y是下午 将知识用谓词表示为：a (?x )(?y) (A(y)→B(x)∧P(x)) (3)新型计算机速度又快，存储容量又大。 解：定义谓词 NC(x)：x是新型计算机 F(x)：x速度快 B(x)：x容量大 将知识用谓词表示为： (?x) (NC(x)→F(x)∧B(x)) (4) 不是每个计算机系的学生都喜欢在计算机上编程序。 解：定义谓词 S(x)：x是计算机系学生 L(x, pragramming)：x喜欢编程序 U(x,computer)：x使用计算机 将知识用谓词表示为： ?(?x) (S(x)→L(x, pragramming)∧U(x,computer)) (5)凡是喜欢编程序的人都喜欢计算机。 解：定义谓词 P(x)：x是人 L(x, y)：x喜欢y 将知识用谓词表示为： (?x) (P(x)∧L(x,pragramming)→L(x, computer))
2 请对下列命题分别写出它们的语义网络： (1) 每个学生都有一台计算机。 解： (2) 高老师从3月到7月给计算机系学生讲《计算机网络》课。 解： (3) 学习班的学员有男、有女、有研究生、有本科生。 解：参例2.14 (4) 创新公司在科海大街56号，刘洋是该公司的经理，他32岁、硕士学位。 解：参例2.10 (5) 红队与蓝队进行足球比赛，最后以3：2的比分结束。 解：
第二章热力学第一定律 1.热力学能就是热量吗? 答：不是，热是能量的一种，而热力学能包括内位能，内动能，化学能，原子能，电磁能，热力学能是状态参数，与过程无关，热与过程有关。 2.若在研究飞机发动机中工质的能量转换规律时把参考坐标建在飞 机上，工质的总能中是否包括外部储能？在以氢氧为燃料的电池系统中系统的热力学能是否包括氢氧的化学能？ 答：不包括，相对飞机坐标系，外部储能为0； 以氢氧为燃料的电池系统的热力学能要包括化学能，因为系统中有化学反应 3.能否由基本能量方程得出功、热量和热力学能是相同性质的参数 结论？ 答：不会，Q U W ?为热力学能的差值，非热力学能，热=?+可知，公式中的U 力学能为状态参数，与过程无关。 4.刚性绝热容器中间用隔板分为两部分，A 中存有高压空气，B 中保持真空，如图2-1 所示。若将隔板抽去，分析容器中空气的热力学能如何变化？若隔板上有一小孔，气体泄漏入 B 中，分析A、B 两部分压力相同时A、B 两部分气体的热力学能如何变化？ 答：将隔板抽去，根据热力学第一定律q u w w=所以容 =?+其中0 q=0 器中空气的热力学能不变。若有一小孔，以B 为热力系进行分析
2 1 2 2 222111()()22f f cv j C C Q dE h gz m h gz m W δδδδ=+++-+++ 只有流体的流入没有流出，0,0j Q W δδ==忽略动能、势能c v l l d E h m δ=l l dU h m δ=l l U h m δ?=。B 部分气体的热力学能增量为U ? ，A 部分气体的热力学能减少量为U ? 5.热力学第一定律能量方程式是否可以写成下列两种形式： 212121()()q q u u w w -=-+-，q u w =?+的形式，为什么？ 答:热力学第一定律能量方程式不可以写成题中所述的形式。对于 q u w =?+只有在特殊情况下，功w 可以写成pv 。热力学第一定律是一个针对任何情况的定律，不具有w =pv 这样一个必需条件。对于公式212121()()q q u u w w -=-+-，功和热量不是状态参数所以不能写成该式的形式。 6.热力学第一定律解析式有时写成下列两种形式： q u w =?+ 2 1 q u pdV =?+? 分别讨论上述两式的适用范围. 答： q u w =?+适用于任何过程，任何工质。 2 1 q u pdV =?+? 可逆过程，任何工质 7.为什么推动功出现在开口系能量方程式中，而不出现在闭口系能量
When while as的区别和用法 when的用法 当主句使用持续性动词时. Dave was eating,when the doorbell rang.门铃响时,大卫在吃饭. 2.一个动作紧接着另一个动作发生. When the lights went out, I lit some candles.灯灭了,我赶紧点上一些蜡烛. 3.谈论生命中的某一阶段,或过去的某段时间. His mother called him Robbie when he was a baby. 在他很小时,他妈妈叫他Robbin. 4.指"每一次" When I turn on the TV, smoke comes out the back. 每当我打开电视,就有烟从后面冒出. while/as 的用法 从句多为进行时,而且为持续性动词. I'll look after the children while you are making dinner. 你做饭,我来照顾孩子. 注意事项: (1) “主短从长”型：主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。 Jim hurt his arm while［when，as］he was playing tennis. 吉姆打网球时把手臂扭伤了。 As［When，While］she was waiting for the train，she became very impatient. 她在等火车时，变得很不耐烦。 (2) “主长从长”型：若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。 但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as：
when 和while的用法区别 ①when是at or during the time that, 既指时间点，也可指一段时间； while是during the time that，只指一段时间，因此when引导的时间状语从句中的动词可以是终止性动词，也可以是延续性动词，而while从句中的动词必须是延续性动词。 ②when 说明从句的动作和主句的动作可以是同时，也可以是先后发生；while 则强调主句的动作在从句动作的发生的过程中或主从句两个动作同时发生。 ③由when引导的时间状语从句，主句用过去进行时，从句应用一般过去时；如果从句和主句的动作同时发生，两句都用过去进行时的时候，多用while引导，如： a. When the teacher came in, we were talking. 当此句改变主从句的位置时，则为： While we were talking, the teacher came in. b. They were singing while we were dancing. ④when和while 还可作并列连词。when表示“在那时”；while表示“而，却”，表对照关系。如： a. The children were running to move the bag of rice when they heard the sound of a motor bike. 孩子们正要跑过去搬开那袋米，这时他们听到了摩托车的声音。 b. He is strong while his brother is weak. 他长得很结实，而他弟弟却很瘦弱。 when，while，as引导时间状语从句的区别 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。 ①Why 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？ ②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。 ③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。 ④The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。 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。 1．从句动作在主句动作前发生，只用when。 ①When 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。 ②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。 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。
1. 已知某一时期内某商品的需求函数为Q =50-5P ，供给函数为Qs=-10+5p。（1）求均衡价格Pe和均衡数量Qe，并作出几何图形。 （2）假定供给函数不变，由于消费者收入水平提高，使需求函数变为Qd=60-5P。求出相应的均衡价格Pe 和均衡数量Qe ，并作出几何图形。（3）假定需求函数不变，由于生产技术水平提高，使供给函数变为Qs=-5+5p。 求出相应的均衡价格Pe 和均衡数量Qe ，并作出几何图形。 （4）利用（1）（2 ）（3），说明静态分析和比较静态分析的联系和区别。（5）利用（1）（2 ）（3），说明需求变动和供给变动对均衡价格和均衡数量的影响. 解答: (1)将需求函数Qd = 50-5P和供给函数Qs =-10+5P 代入均衡条件Qd = Qs ,有: 50- 5P= -10+5P 得: Pe=6 以均衡价格Pe =6 代入需求函数Qd =50-5p ,得: Qe=20 所以,均衡价格和均衡数量分别为Pe =6 , Qe=20 (图略) (2)将由于消费者收入提高而产生的需求函数Qd=60-5p 和原供给函数 Qs=-10+5P, 代入均衡条件Q d= Qs ,有: 60-5P=-10+5P 得Pe=7 以均衡价格Pe=7代入Qd方程，得Qe=25 所以,均衡价格和均衡数量分别为Pe =7 , Qe=25 (图略) (3) 将原需求函数Qd =50-5p和由于技术水平提高而产生的供给函数Q =-5+5p , 代入均衡条件Qd =Qe ,有: 50-5P=-5+5P得Pe= 5.5 以均衡价格Pe= 5.5 代入Qd =50-5p ,得22.5 所以,均衡价格和均衡数量分别为Pe=5.5 Qe=22.5 (4)所谓静态分析是考察在既定条件下某一经济事物在经济变量的相互作用下所实现的均衡状态及其特征.也可以说,静态分析是在一个经济模型中根据所给的外生变量来求内生变量的一种分析方法.以(1)为例,在图中,均衡点 E 就是一个体现了静态分析特征的点.它是在给定的供求力量的相互作用下所达到的一个均衡点.在此,给定的供求力量分别用给定的供给函数Q=-10+5P 和需求函数Q=50-5P表示，均衡点具有的特征是:均衡价格P=6 且当P =6 时,有Q= Q d= Qe =20 ，同时,