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慧通职场英语综合教程2答案1、This species has nearly （）because its habitat is being destroyed. [单选题] *A. used upB. died out(正确答案)C. gone upD. got rid of2、( ) She keeps on learning English all the time. So far, she______three books of New Concept English. [单选题] *A. has learned(正确答案)B. have learnedC. had learnedD. learn3、( ) ----Would you like___ tea? ----No, thanks. I have drunk two____. [单选题] *A. any, bottles of orangeB. some, bottles of orange(正确答案)C. many, bottles of orangesD. few, bottle of oranges4、48．—________ is your new skirt, Lingling?—Black. [单选题] *A．HowB．What colour(正确答案)C．WhichD．Why5、_______ hard, _______ you’ll fail in the exam. [单选题] *A. Studying; forB. Study; or(正确答案)C. To study; andD. Study; and6、I didn't hear _____ because there was too much noise where I was sitting. [单选题] *A. what did he sayB. what he had said(正确答案)C. what he was sayingD. what to say7、You should take the medicine after you read the _______. [单选题] *A. linesB. wordsC. instructions(正确答案)D. suggestions8、Tom didn’t _______ his exam again. It was a pity. [单选题] *A. winB. pass(正确答案)C. beatD. Fail9、Nearly everything they study at school has some practical use in their life, but is that the only reason _____ they go to school? [单选题] *A. why(正确答案)B. whichC. becauseD. what10、Mary's watch is more expensive than _____. [单选题] *A. Susan's(正确答案)B. that of Susan'sC. that of SusanD. Susan11、_______ songs is my favorite. [单选题] *A. To Singing EnglishB. Singing English(正确答案)C. Singings EnglishD. Sing English12、You can ask（）is on duty there tonight. [单选题] *A. WhatB. whomC. whoever(正确答案)D. whomever13、29．There is a book in your left hand. What’s in your ___________ hand? [单选题] * A．the othersB．other (正确答案)C．anotherD．others14、Tom didn’t _______ his exam again. It was a pity. [单选题] *A. failB. winC. pass(正确答案)D. beat15、31．That's ______ interesting football game. We are all excited. [单选题] *A．aB．an(正确答案)C．theD．/16、--All of you have passed the test!--_______ pleasant news you have told us! [单选题] *A. HowB. How aC. What(正确答案)D. What a17、—Who came to your office today, Ms. Brown?—Sally came in. She hurt ______ in P. E. class. （）[单选题] *A. sheB. herC. hersD. herself(正确答案)18、24．Kitty’s father ______ a policeman since 2 He loves helping people. [单选题] * A．isB．wasC．has been (正确答案)D．have been19、Actually, we don't know whether this news comes from a reliable（）or not. [单选题] *A. source(正确答案)B. originC. basisD. base20、--Do you have a _______?--Yes, I _______ at a clothes store. [单选题] *A. work; workB. work; jobC. job; jobD. job; work(正确答案)21、—Whose book is it? Is it yours?—No, ask John. Maybe it’s ______.（）[单选题] *A. hersB. his(正确答案)C. he’sD. her22、The car _______ after forty minutes driving, so he didn’t have the interview on time. [单选题] *A. broke down(正确答案)B. broke inC. broke outD. broke up23、The teachers don't make us wear a school uniform and we can wear _____ we like. [单选题] *A. anyB. thatC. asD. what(正确答案)24、Sometimes only（）10 out of 500 or more candidates succeed in passing all the tests. [单选题] *A. as many asB. as few as(正确答案)C. as much asD. as little as25、In the closet（）a pair of trousers his parents bought for his birthday. [单选题] *A. lyingB. lies(正确答案)c. lieD. is lain26、I walked too much yesterday and （）are still aching now. [单选题] *A. my leg's musclesB. my leg muscles(正确答案)C. my muscles' of legD. my legs' muscles27、Nearly two thousand years have passed _____ the Chinese first invented the compass. [单选题] *A. whenB. beforeC. since(正确答案)D. after28、Bob used ______ on the right in China, but he soon got used ______ on the left in England.（）[单选题] *A. to drive; to driveB. to drive; drivingC. to driving; to driveD. to drive; to driving(正确答案)29、--Do you know _______ girl with long curly hair?--Yes. She is Mary. She plays _______ piano very well. [单选题] *A. a; /B. the; /C. the; the(正确答案)D. a; the30、Something must be wrong with the girl’s _______. She can’t hear clearly. [单选题] *A. ears(正确答案)B. noseC. armsD. eyes。
Book2 Unit 1Tales of the unexplained1．witness vt.当场见到，目击；见证；是发生……的地点(或时间、组织等)；……就是证据；看……就知道；n.目击者；证人；证据归纳拓展(1)witnessfor为……作证witnesstosth./doingsth.作证证明某事/做某事(2)(a)witnesstosth.某事的证人inwitnessof作为……的证据Thatevening，ourgroupspenthourstalkingaboutwhatwehadwitnessed.(2009·浙江，完形填空) 那天晚上，我们组花了数小时讨论我们所看到的事情。
活学活用(1)根据语境翻译witnessThewitness①______whowitnessed②________theincidentgavewitnesses③________tothepo liceandpromisedtobeawitness④________.(2)Thepolicefoundthe__________themurdercase.警察找到了那个谋杀案的目击者。
(3)Recentyearshave____________agrowingsocialmobility.近年来人们的社会流动性越来越大。
(4)Hewitnessedto________themanentertheroom.A．haveseenB．havingseenC．seeD．seeing2．puzzle n．谜；疑问；v.迷惑；使困惑________adj.令人迷惑的________adj.困惑的；迷惑不解的__________n．迷惘；困惑归纳拓展puzzleover/about绞尽脑汁；苦思冥想inpuzzlement迷惘地Shestaredathim，puzzledatfirst, thenangryandfinallyalookofhelplessnesscameoverher.她盯着他，先是不解，然后是愤怒，最后脸上是无助的表情。
Unite2 （有答案）Text A (P30-P32)Grammaire (P36-P37)Text B (P39-P4)Text AⅡ Transformez les phrase suivantes selon le modèle.1.étre loin de + inf.(1)Nous n’avons pas encore terminé nos recherches.Nos recherches sont loin d’être terminées.(2)Paul n’a pas encor e fini ses devoirs.Ses devoirs sont loin d’être finis.(3)Il veut pas laisser tomber son espoir.Son espoir est loin d’être laissé tomber.(4)Elles n’ont pas encore résolu le problème de matière.Le problème de matière est loin d’être résolu.2.donner satisfaction à(1)Tout le monde est satisfait de ces mesures.Ces mesures donnent satisfaction à tout le monde.(2)Notre chef n’est pas content de ce projet.Ce projet ne donne pas satisfaction à tout le monde.(3)Les habitants sont contentes de cette décision.Cette décision donne satisfaction aux habitants.(4)Les touristes sont contents de cet agent de police.Cet agent de police donne satisfaction aux touristes.3.Ce que ... c’est de + inf.(1)Patricia veut changer complètement son mode de vie.Ce que Patricia veut, c’est de ch anger complètement son mode de vie.(2)Louis désire partir en vacances avec ses amis.Ce que Louis désire, c’est de partir en vacances avec ses amis.(3)On espère se revoir le plus tôt possible.Ce qu’on espère, c’est de se revoir le plus tôt possible.(4)Michel et sa femme veulent visiter tous les musées de notre ville.Ce que Michel et sa femme veulent, c’est de visiter tous les musées de notre ville. III Compléter le tableau suivantl’action celui qui fait l’action le nom ou le résultat de l’act ionétudier un étudiant une étudeemployer un employeur un emploitravailler un travailleur un travailparticiper un participant une participationchanter un chanteur une chansonvoyager un voyageur un voyagedemander un demandeur une demandechercher un chercheur une rechercheécrire un écrivain un écritIV Complétez avec un des verbes donnés : limiter , enfermer ,arrêter ,cesser ,renverser ,détruire1.L’hôpital où il est né a été détruit complètement par la guerre .2.Lès soldats ont enfermé/enfermaient des ennemis dans un cabinet avant que leurchef ne vienne.3.si la pluie cesse , j’irai à la librairie pour acheter quelques livres sur la technologiede pointe .4.nous avons arrêté un agent de police pour lui demander notre chemin .5.Faute d’attention , le client a renversé un verre sur la table .6.Il nous faut limiter la vitesse de voiture sur cette toute oùil y a tropd’automobiles.7.Ses études universitaires ont été arrêtées à cause d’une maladie grave .8.Tous les enfants ont cessé de crier dès que leur maîtresse était entrée dans la salle . V Traduisez en français :充满希望être plein d’espoir政府高级官员des hauts fonctionnaires du gouvernement幸运逃脱se sauver heureusement新的教育制度un nouveau système de l’éducation从不批评孩子ne jamais critiquer les enfants重新打开大门ouvrir de nouveau la porte修建一座城堡construire un château老板与员工的争论la discussion entre le patron et les employésⅥ.Complétez avec celui qui, que, dont ou ce qui, que, dont, etc.Invite-le avec ses parents!Fils: Papa, est –ce que je peux inviter des amis samedi soir ?Père: Fais ce que tu veux !Fils: On peut faire des brochettes dans le jardin?Père: Préparez ce qui vous plaît!Fils:Je peux t’emprunter un peu d’argent? Je dois aller au supermarché pour faire des courses.Père: Mon portefeuille est sur mon bureau. Prends ce dont tu as besoin.Fils: Dis! Je peux inviter tous mes amis?Père: Invite tous ceux que tu veux.Fils: Même celui qui s’est disputé avec toi l’autre jour?Père: C’est celui dont le père est inspecteur des impôts?Fils: Oui.Père: Alors invite-le avec ses parents .Ⅷ.thème1.罢工结束时，老板满足了工人们的要求。
绿野仙踪阅读测试题(及答案) 绿野仙踪阅读测试题(及答案)第一章：多萝茜的家1·多萝茜住在哪个国家？答案：多萝茜住在美国堪萨斯州。
2·多萝茜的最好朋友是谁？答案：多萝茜最好的朋友是她的小狗托托。
3·多萝茜的家被哪个自然灾害卷走了？答案：多萝茜的家被龙卷风卷走了。
第二章：神奇的旅程开始1·多萝茜是如何进入奇幻世界的？答案：多萝茜被龙卷风卷到了奇幻世界。
2·多萝茜在奇幻世界中遇见了哪位巫师？答案：多萝茜遇见了绿野仙踪的巫师。
3·多萝茜希望巫师能帮她做什么？答案：多萝茜希望巫师能帮她回到家。
第三章：黄金大道1·多萝茜在黄金大道上遇见了哪个角色？答案：多萝茜在黄金大道上遇见了稻草人。
2·稻草人希望巫师能给他什么？答案：稻草人希望巫师能给他一个智慧的大脑。
3·多萝茜和稻草人一起前往哪个城市？答案：多萝茜和稻草人一起前往翠绿城。
第四章：银色森林1·多萝茜在银色森林中遇见了哪个角色？答案：多萝茜在银色森林中遇见了铁皮人。
2·铁皮人希望巫师能给他什么？答案：铁皮人希望巫师能给他一个心脏。
3·多萝茜、稻草人和铁皮人一起前往哪个城市？答案：多萝茜、稻草人和铁皮人一起前往锡切姆城。
第五章：狮子王国1·多萝茜、稻草人、铁皮人在狮子王国中遇见了谁？答案：多萝茜、稻草人、铁皮人在狮子王国中遇见了懦弱的狮子。
2·懦弱的狮子希望巫师能给他什么？答案：懦弱的狮子希望巫师能给他勇气。
3·多萝茜、稻草人、铁皮人和懦弱的狮子一起前往哪个城市？答案：多萝茜、稻草人、铁皮人和懦弱的狮子一起前往神秘城市。
第六章：巫师的真相1·在神秘城市，巫师告诉多萝茜们真相是什么？答案：巫师告诉多萝茜们真相是他是一个骗子，没有真正的魔法。
2·多萝茜和她的朋友们决定去找谁帮助她们？答案：多萝茜和她的朋友们决定去找女巫帮助她们。
新视野大学英语（第2 版）读写教程第 3 册史上最全的《新视野大学英语(第2版)读写教程》全四册完整版答案!! 剩余其他三册答案,见我 yeah163_a 文库。
Ps:亲!给好评,有送财富值哦! #＾_＾!!第一章Unit 1 答案Section AIII1 beneath2 disguised3 whistles4 restrain5 grasp6 longing7 praying8 faithful 9 pledge 10 drainIV 1 tell … on you 2 track down 3 work it out 4 picking on me 5 reckoned with6 call on7 on his own8 get through9 in disguise 10 revolves aroundV G O D I K L B F A NVI1 advise2 level3 problems4 necessity5 skills6 experience7 solution8 value 9 tool 10 mannerVII1 air-conditioned( 装空调的；有冷气的)2 handmade （手工制作的）3 thunderstruck （非常吃惊的）4 heartfelt （衷心的；诚挚的）5 data-based （基于数据的）6 self-employe d （自主经营的）7 custom-built （定制的；定做的）8 weather-beaten （饱经风霜的）VIII1. well-informed （对……非常熟悉的）2 new-found （新获得的）3 hard-earned （辛苦挣得的）4 soft-spoken （说话温柔的）5 newly-married （新婚的）6 widely-held （普遍认为的）7 well-meant （出于好意的）8 well-educated （受过良好教育的）IX 1 no matter how different it may seem form any other substance2 no matter what a woman tries to do to improve her situation3 no matter what excuse he gives4 no matter what anyone else may think5 no matter how they rewrite historyX 1 just as we gained famein victory, we lost nothingin defeat2 just as the head teacherplays a significant role in the school, Jane plays a significant role fleader in the classroom.3 whoever was out there obviously couldn ’t see him just as he couldn ’t see them.4 she has been searching all her life for the perfect chocolate just as I have been searching for the perfect beer.5 you can make those kinds of comparisons just as you were doing the analyses a minute ago.XI1. No matter how experienced a speaker youare, and how well you have prepared your speech,you will have difficulty making a speech at such anoisy reception.2. Just as all his sist er ’ sfriends cared about him, Jimmy cared about them.3. Car manufacturers stamp a vehicle identification number at several places on new carsto help track down stolen vehicles.4. If you dare tell on me when the teacher gets back I won ’t say a wordto yo u any more.5. Some elderly people prefer to live on their ownwhile the great majority choose to live with their children.6. Here is something that needs to be reckoned with: how to get the necessary finances to establish the company.XII1. 每当有人帮了你，无论事情大小，无论他地位高低，你都应该对他说声“谢谢”。
大学英语精读第二册〔第三版〕book2Unit1答案1. bare2. Empty3. Empty4. Bare5. Empty6.empty二〕三〕1. host2. sprang up/rang out3. Impulse4. came to5. track down6. Unexpected7. Outgrow8. Widened9. Shortly10. emerge / spring up11. at the sight of12. made for13. Crisis14. colonial四〕1. Jimmy has outgrown the shirts his aunt made for him a few years ago.2. Does the doctor think the elderly lady is likely to survive the operation / it is likely that the elderly lady will survive the operation?3. The other day your cousin paid us an unexpected visit.4. Don't you see the nurse motioning us to be silent?5. Her face lit up with joy at his return.6. The sound of her footsteps grew fainter as she walked farther away.五〕1.Additional advantageousAnxious conditionalCourageous curiousDangerous educationalEmotional famousIndustrial intentionalMedical mountionouMusical mysteriousNational occasionalPersonal practical2.Heated coloredpigtailed giftedbearded pointedexperienced agedskilled diseased六〕1.The people questioned gave very different opinions on the issue.2. Can you see the man climbing on that rock?3. Several days passed before they came up with a satisfactory solution to the problems discussed.4. We were woken early by the sound of the birds singing.5. The chairman made it clear that those objecting should explain their reasons.6. After a day’s work, I felt I had little energy left.7. I knew of some of the athletes taking part.8. The success obtained surprised those who had given up the project as impossible.七〕1. During the time that2. As long as3. Although4. as long as5. whereas6. Although7. whereas8. Although1. They frightened the child into telling the truth.2. He tricked her into marrying him by pretending that he was the son of a millionaire.3. My tactless words forced the old gentleman into buying something he could not possibly afford.4. He finally talked me into accepting his terms.5. The girl persuaded her father into giving up smoking.6. Their severe criticism shocked her into realizing her selfishness.1. Guests are to be back in the hotel by twelve o’clock.2. An investigation is to be made next week.3. I am to meet them at the airport.4. You are to finish your homework before you watch TV.5. The medicine is to be taken three times a day after meals.6. Bob and Susan are to get married in October八〕九〕十〕1.她砰地关上门，一声不吭地走了，他们之间那场争执就此完毕。
Part ⅢListening ComprehensionA．答案与详解Section A11.【答案与详解】C。
替换题。
女士说前儿天碰到Sally时几乎都认不出她了。
男士说Sally过去有些out of shape(变形，走样)，之后问她现在是不是减了很多体重。
本题中的out of shape与答案中的overweight进行了替换。
所以C是正确答案。
12.【答案与详解】D。
场景题。
本题询问对话发生的地点，四个选项结构相同，都是介词结构。
场景题的解题关键就是场景所对应的线索词。
本题中根据女士所说的reservation(预订，预留)和男士所说的reserve和room，可以判断出对话发生的地点是旅馆。
所以D是正确答案。
13.【答案与详解】B。
替换题。
针对女士的疑问，男士回答“I’d just not worry”，之后进行了详尽的解释说明。
not worry 对应答案中的confidence。
所以B是正确答案。
14.【答案与详解】A。
替换题。
男士认为女士在最近两周都是满负荷工作，之后提出建议：“I think you really need to go out and get some fresh air and sunshine.”(我认为你真的应该出去晒晒太阳、呼吸—下新鲜空气。
) go out and get some fresh air and sunshine对应答案中的short break。
所以A是正确答案。
15.【答案与详解】D。
but题。
针对女士的疑问，男士回答：“He’s been sick all week，but I’venever felt better in my life.”(他已经病了一周了，但是我却感到前所未有的健康。
)所以D 是正确答案。
16.【答案与详解】B。
替换题。
男士问女士是不是上个月搬进新居时卖掉了所有家具，女士回答“just the useless pieces”(只是卖掉了那些没有用的家具)，对应答案中的some furniture，所以B是正确答案。
流畅英语口语教程第二版第3册课后练习题含答案1. IntroductionThe second edition of Fluent English Oral Tutorial consists of three volumes, each contning various exercises that can help learners improve their speaking skills. In this document, we’ve provided the exercises and answers for the third volume of the series.2. Exercise 1: Pronunciation Practice1.Choose a word from the list below and read it aloud, payingparticular attention to the underlined sound:–Smile, slice, slide, slip, sleep–Sun, son, sing, sung, soon–Far, fr, for, fur, fireAnswer:–Smile–Sun–Fr2.Identify the underlined sound in the following words:–Cat, cut, caught, coat–Well, will, whale, wall–Lake, luck, look, lackAnswer:–/æ/–/w/–/ʊ/3. Exercise 2: Vocabulary Practice1.Fill in the blank with the correct word from the list below:–Instead, although, although, however, despite–Strong, happy, cheap, busy, safe–She loves to travel by trn, ______ it can be a bit slow.–He didn’t speak English ______ he had been studying it for years.–She decided to go to the party anyway, ______ she was feeling tired.–He is a ______ swimmer who can easily swim long distances.–The traffic was heavy, but ______ she arrived at the meeting on time.Answer:–Although–Although–Despite–Strong–However2.Match the adjectives on the left with the appropriatepreposition on the right:–Proud–Interested–Afrd–Familiar–Ashamed–Of–In–About–With–ToAnswer:–Proud of–Interested in–Afrd of–Familiar with–Ashamed of4. Exercise 3: Speaking Practice1.Discuss the following questions with a partner:–What kind of music do you like to listen to, and why?–Have you ever been to a concert or live performance?If so, describe your experience.–Do you think music can have a positive effect on people’s mood? Why or why not?Answer:Answers to this exercise will vary depending on the learner’s responses to the questions.plete the following sentences about yourself, using the words from the list below:–Passionate, friendly, creative, organized, motivated–I am ______ about learning new things.–My friends often describe me as ______.–In my free time, I enjoy ______ activities, like pnting or writing.–I am good at ______ my work schedule and getting things done on time.–When I face a challenge, I am ______ to find a solution.Answer:–Passionate–Friendly–Creative–Organizing–Motivated5. ConclusionIn this document, we’ve provided the exercises and answers for the third volume of the Fluent English Oral Tutorial series. These exercises can be useful for learners looking to improve their speaking skills and expand their vocabulary.。
一、根据首字母填写单词(单词拼写)1. Climate change is a g________ issue that requires all the countries to make joint efforts in cutting down carbon emission (碳排放). (根据首字母单词拼写)2. There is no doubt that Germany and Japan were to b________ for WWII as they invaded other countries and cruelly killed a lot of innocent people. (根据首字母拼写单词)3. Climate change is a g_________ issue that concerns us all and therefore countries should work together to fight against it. (根据首字母单词拼写)二、根据汉语意思填写单词(单词拼写)4. ________(责备) for the breakdown of the school computer network, he was in low spirits. (根据汉语提示单词拼写)5. The threat of _____(全球) warming will force the U.S. to slow down its energy consumption. (根据汉语提示拼写单词)6. For a time he was looked on as a ________ (有前途的) writer. (根据汉语提示单词拼写)三、根据中英文提示填写单词(单词拼写)7. We can observe that artificial intelligence has already made an i________ (影响) on our lives in many ways. （根据中英文提示填空）8. One h________(精彩之处) of their trip was being able to see many different creatures. (根据中英文提示填空)四、完成句子9. 野生动物在自然界中扮演着重要的角色，那就是我们应该增强对它们的保护意识的原因。
龙书第二章答案SnoozeCS 431, Assignment 3, Book Questions on Chapter 2Plus One Other QuestionQuestions that you need to answer are listed below, and some solutions or partial solutions are also given. The solutions are not presented as the only possible answers, and what is given may not be complete. It may only be a starting point for thinking about a complete, correct answer. Your goal in working the problems should be to come up with a solution, and if in doubt about your answer, compare with what’s gi ven here. In theory, even if your answer is not exactly the same, you should see the sense or understand the direction of the suggestions. If your answer is at odds with what I have suggested you might want to check with me. It is possible that I am off base. It is also possible that you need some things clarified.Book problems: 2.1, a-c; 2.2, a-e; 2.3; 2.4, a-e, and 2.8. Suggested answers to these questions are given after the following question.Last problem: There is an additional problem that is not from the book. It is stated here. Implement Java code that will correctly translate infix expressions with + and – (no parentheses and no other operators) to postfix expressions. A problem solution is given in the book in C code, so your task is mainly one of adaptation. A starting point for this problem is posted on the Web page. You may use the file InfixToPostfixCut.java as given and simply add the needed methods. You can also do the problem from scratch if you want to. I think it would be preferable if you left your implementation recursive rather than changing it to a loop, but that is your choice. Hand in a printout of the methods you added along with your answers to the problems listed above.Starting points for thinking about solutions:2.1. Consider the following context-free grammarS → S S + (1)S → S S * (2)S → a (3)a) Show how the string aa+a* can be generated by this grammar.Production (3) allows you to generate a string S0 which consists of a.Using S0 as a starting point, production (1) allows you to generate a string S1 which consists of aa+.Production (3) again allows you to generate a string S2 which consists of a.Then production (2) allows you to generate a string S3 = S1S2* = aa+a*.b) Construct a parse tree for this string.c) What language is generated by this grammar? Justify your answer. Assuming a is an identifier for a numeric value, for example, then the grammar generates a language consisting of all possible arithmetic combinations of a using only the operations + and * and postfix notation. (No particular justification is given. Check to see if you agree.)2.2. What language is generated by the following grammars? In each case justify your answer. (No justifications are given.)a) S → 0 S 1 | 0 1All strings divided evenly between 0’s and 1’s, with the sequence of 0’s coming first and the sequence of 1’s coming second.b) S → + S S | - S S | aThis is the prefix analog to question 2.1.c) S → S ( S ) S | εThis will generate arbitrary sequences of adjacent and nested, matched pairs of parentheses.d) S → a S b S | b S a S | εAll possible strings containing equal numbers of a’s and b’s, with the a’s and b’s arranged in no particular order.e) S → a | S + S | S S | S * | ( S )I don’t see a pattern to this that I can verbally describe.2.3. Which of the grammars in Exercise 2.2 are ambiguous?To show ambiguity it is sufficient to find any single string that can be parsed in more than one way using the grammar. No such strings spring immediately tomind for the grammars of a through d. (That does not mean that there aren’t any.) However, e is clearly ambiguous. Let the string S + S * be given. Here are two possible parsings:2.4. Construct unambiguous context-free grammars for each of the following languages. In each case show that your grammar is correct. (Correctness is not shown.)a) Arithmetic expressions in postfix notation.list → list list + list → list list – list → digitlist → 0 | 1 | 2 | … | 9b) Left-associative lists of identifiers separated by commas.list → list, id list → idc) Right-associative lists of identifiers separated by commas.list → id, list list → idd) Arithmetic expressions of integers and identifiers with the four binary operators +, -, *, /.Add the following rule to the grammar given at the end of section 2.2: factor → identifiere) Add unary plus and minus to the arithmetic operators of (d).Add the following rules to the grammar:factor → +factorfactor → -factor2.8 Construct a syntax-directed translation scheme that translates arithmetic expressions from postfix notation to infix notation. Give annotated parse trees for the inputs 95-2* and 952*-.Here is a simple grammar that can serve as a starting point for the solution of the problem:string → digit string operator| string digit operator| digitdigit →0 | 1 | 2 | … | 9operator → * | / | + | -Here is an annotated parse tree of the first expression:The first production applied in forming this tree was: string → string digit operator. Notice that it would have been just as possible to apply the production: string → digit string operator. If that had been done you would have then had to parse the string “5-2”. This result would not parse and it would be necessary to backtrack and choose to apply the other production. At the next level down it doesn’t matter which production is chosen.In this example there is no choice about which production to apply first. At the second level there is a choice but it doesn’t make a difference. The lack of choice at the first level illustrates clearly how you could tell whether or not the production you have chosen is the correct one, assuming you could look that far ahead: If the string that you have parsed on the right hand side does not end in an operator, then the production choice is not correct. It is also possible to see that if you could specify the order in which productions are tried, you could avoid backtracking. If you always tried to parse using this production first: string string digit operator and tried the other one if that one failed to apply, you would avoid backtracking. But again, such an approach is not allowed. The question of backtracking is discussed on pages 45 and 46 of the book. The upshot of the matter is that this grammar isn’t suitable for predictive parsing.There is another matter that will require a change in the grammar so that a syntax-directed translation scheme can be devised. At the top of page 39 in the book the term “simple” is defined as it applies to a syntax-directed definition. The requirement is that the order of non-terminals on the right hand side of a production agree with the order of the corresponding symbols generated as the desired output. Other symbols or terminals may come before, between, or after the output for the non-terminals. Under this condition the output can be generated from a depth first traversal of the annotated tree. The problem with the grammar given above is that all of the operators are symbolized using the non-terminal “operator”. However, in the translation from postfix to infix, it is the position of the operator that changes. That means that even though tedious, for practical reasons the productions have to be rewritten with the operator symbols in-line as terminals:string → digit string *| digit string /| digit string +| digit string –| string digit *| string digit /| string digit +| string digit –| digitdigit →0 | 1 | 2 | … | 9The problem only gets better and better, or worse and worse, depending on your point of view. Postfix notation does not require parentheses. The relative positions of the operands and operators unambiguously determine the order of operations. This means that an arbitrary postfix expression may enforce an order of operations which would not occur naturally in an unparenthesized infix expression. In particular, 95-2* does not translate to 9 – 5 * 2, where the multiplication would be done first. It translates to (9 – 5) * 2. It is not an attractive proposition to try and implement a translation scheme that would only insert parentheses when needed. It is much more convenient to fully parenthesize the infix translation whether needed or not. The unneeded parentheses do not adversely affect the meaning of the arithmetic.Having said all of the above, here is my suggested syntax-directed translation scheme, that is, a context-free grammar with embedded semantic actions that will generate the infix translation of a postfix input:string →{print(“(“)} digit {print(“*”)} string * {print(“)”)}| {print(“(“)} digit {print(“/”)} string / {print(“)”)}| {print(“(“)} digit {print(“+”)} string + {print(“)”)}| {print(“(“)} digit {print(“-”)} string - {print(“)”)}| {print(“(“)} string {print(“*”)} digit * {print(“)”)}| {print(“(“)} string {print(“/”)} digit / {print(“)”)}| {print(“(“)} string {print(“+”)} digit + {print(“)”)}| {print(“(“)} string {print(“-”)} digit - {print(“)”)}digit →0 {print(“0”)}| 1 {print(“1”)}etc.The parse tree for 95-2* showing semantic actions follows.And here is the parse tree for 952*- showing semantic actions.If there are no mistakes in the parse trees, traversing them in depth-first order and executing the print statements as you go should cause the correct, parenthesized, infix translation of the postfix input to be emitted.。
