外貿(mào)函電課程教案設計

1、外貿(mào)英語函電課教案學期：2008-2009學年學時：_j40系 （部）：外國語學院教 研 室：專業(yè)英語教研室授課教師： 安然授課班級所在系授課班級授課班級所在系授課班級外國語學院2006英語教學目的：本課程是英語（水產(chǎn)貿(mào)易英語）專業(yè)的核心課程。通過本課程的學習，熟悉 翻譯和寫作外貿(mào)業(yè)務中各類書信，掌握外貿(mào)業(yè)務中英語術(shù)語、縮略語、慣用句型和表達 方法。教學手段：教師授課和互動式教學結(jié)合，教學方法：復習，導入，教師講解，學生練習iEnglish Business Correspondence 教案章 節(jié)：Preface2課時教學目的：掌握商務溝通的基本原則及英文書信的寫作格式教學任務： Part

2、One: Principles of Good CommunicationThe Structure of Business LettersThe forms of business letters Addressing an envelope 重點、難點：1. The Three Features f Business Communication2. The Basic Principles of Business Letter Writing3. The three forms4. The principles of addressing envelopes教學內(nèi)容提要：The Three

3、 Features:1. It has its own special language style and words.2. It is full of business termination, abbreviations and abbreviated phrases.3. It has close connections with international business practice.The 7 c ' s: consideration courtesy clarity conciseness concreteness correctness completeness

4、The Standard Parts:The Optional Parts:1.the letterhead1.the references2.the date2.the attention line3.th inside address3.the subject line4.the salutation4.the enclosure5.the body of the letter5.the postscript6.the complimentary close6. the carbon copy notation7.the signature7. the identification lin

5、e復習思考題、作業(yè)：What is the relations between EBC and foreign trade?Page No.10 Ex. I課后小結(jié)：1.Grasp the unique characteristics of EBC2. The difference between social communications and EBC3. Grasp the Standard Parts and the Optional Parts of EBC3English Business Correspondence 教案章 節(jié)：Preface 2課時教學任務：Skill Tra

6、ining重點、難點：1. Arrange a letter in proper form as they should be set outin a letter2. How to write self-introduction lettersThe Structure of Business Letters1-1 The full blocked style1-2 The modified blocked style1-3The indented style1-4The Semi-blocked style with indented-paragraphs open punctuation

7、 close punctuationAddressing envelopes : three requirements:1. accuracy2. clearness3. appearance4. Explain C/O復習思考題、作業(yè)：Page No.10 Ex. II#課后小結(jié)：Grasp the three forms of EBCHow to fill in an envelope?Write a letter to an exporter and address an envelopeEnglish Business Correspondence 教案 章 節(jié)： Chapter On

8、e Establishing business relations 教學任務：Letter 6 Letter 7重點、難點：1. Self-introduction letters2. transferring business relations3. Credit inquiries1. owe one' s name and address to sb2. Commercial Counsellors Office3. inform sb. of sth./ inform sb. that/ be informed that4. be in a market for sth.5.

9、textiles6. avail7. approach = get in touch with8. establish business relations with sb.9. a state-operated corporation10.handle11. acquaint sb with sth12. be well acquainted with sth復習思考題、作業(yè)：Page No.12 Ex.I課后小結(jié)：熟練掌握自薦信的寫作及其慣用表達法。自薦信的寫作要點=(1)說明情報來源(2)說明寫信目的(3)自報家門(4)說明經(jīng)營方針或政策(5)說明資信狀況English Business

10、 Correspondence 教案章 節(jié)：Chapter One Establishing business relations 教學目的：掌握建交信函的寫作內(nèi)容、寫作方法及相關(guān)句型和詞匯。教學任務：Letter 1 Letter 2重點、難點：1. Introduction of your company and its businessscope2. Information on products1. the leading importers= the largest = the principal2. engage in3. enjoy a good reputation.4. sp

11、ecific requirements = details5. at competitive prices6. reasonable price7. favorable price8. enclose9. favor sb. with inquiries for your specific requirements10. Inquiry Note11. attach12. keenest quotation復習思考題、作業(yè)：Page No.13 II課后小結(jié)：熟練掌握轉(zhuǎn)移貿(mào)易關(guān)系書信的撰寫及其慣用表達法轉(zhuǎn)移貿(mào)易關(guān)系：(1)說明情報來源(2)明確介紹貿(mào)易關(guān)系轉(zhuǎn)移的對象(3)結(jié)束語5English

12、 Business Correspondence 教案章 節(jié)： Chapter One Establishing business relations教學任務：Letter 2 , 3重點、難點：1. The first touch2. The reply to the letter you have received教學內(nèi)容提要：1. cooperation2. be desirous of doing sth = be desirous to do sth3. have a good connection4. be obliged if5. be pleased if6. be grate

13、ful if 7. to appreciate it if 8. capable and reliable9. on this respect10. appreciate11.long-standing and high reputation12 .expand = enlarge = extend13 .provide sb with sth= supply sb with sth= furnish sb with sth14 .give sb complete(entire , full ) satisfaction15 .financial position = credit stand

14、ing= financial status= trade reputation16 .refer sb to復習思考題、作業(yè)：Page No.13 Ex. III課后小結(jié)：熟練掌握建立業(yè)務關(guān)系書信的撰寫及其慣用表達法，了解獲取信息、如何與國外客戶接洽的渠道。章 節(jié)：Chapter One Establishing business relations教學任務：Letter 4 Exercises on page 12重點、難點：1. the source the information2. your intention for export or import1. CCPIT2. be in

15、good relations with sb = be well connected with sb3. be interested in sth4. be interested in doing sth5. be interested to do sth6. specifications7. sales possibilities8. at your end = in your place= in your district= in your area復習思考題、作業(yè)：Page No.14 Ex.IV課后小結(jié)：熟練掌握建立業(yè)務關(guān)系書信的撰寫及其慣用表達法，了解國外 客戶資信狀況的渠道及資信狀

16、況調(diào)查信的主要內(nèi)容。7English Business Correspondence 教案章 節(jié)：Chapter One Establishing business relations教學任務：Skill Training重點、難點：1. Write a letter to importer for establishment of business relations2. write a letter to a bank, asking for all information about the importer將學生分為四組（進口商一出口商）進行建立業(yè)務關(guān)系的實際案例操作，各 組推薦合格書

17、信并做分析、講解，通過對照比較，大家講評選出優(yōu)秀作品。目的通過案例分析，加強學生對建立業(yè)務關(guān)系書信的深入了解，提高學生的 分析判斷能力，培養(yǎng)學生的實際應用能力。Training Situations:Mr.Thomas, the managerof Freeman & Sons Company,wants to import some silk products from China. He has learned the name and address of China National Silks Import & Export Corporation on the We

18、b. Now he is going to write a letter to China National Silks Import & Export Corporation to get some more information.復習思考題、作業(yè):Page No. 15 Ex.VIio課后小結(jié)：大部分同學能掌握業(yè)務關(guān)系書信的寫作技巧，能比較準確的表達清楚信的宗旨，運用得當?shù)恼Z言；但也有少數(shù)同學對商務英語慣用法及基礎語法掌握得不夠理想，還需要加大力度多作練習。English Business Correspondence 教案章 節(jié)：Chapter 2 Enquiry教學目的：掌握

19、詢盤信函的翻譯和寫作、相關(guān)句型和詞匯。教學任務：Letter 1重點、難點：1. general enquiry2. specific enquiry1. happens to be = happen to coincide2. sample books3. effect delivery4. material and workmanship5. place an order with sb for sth6. all necessary information7. delivery date8. on the terms and conditions9. by return10. worka

20、ble prices11. on a substantial scale12. learn from13. intend to do sth復習思考題、作業(yè)：Page 28 No.Ex.I課后/J、結(jié)： A specific enquiry should be included the following parts:1 .the reason of the letter2 .state your detailed enquiry3 .give the hints (mention the most important terms)114 .the closing sentence of th

21、e letter章 節(jié)：Chapter 2 Enquiry教學任務：Letter 2, 4重點、難點： Making familiar with inquiry lettersExpressions on making inquiries教學內(nèi)容提要：1. be in receipt of2. of all descriptions3. quote4. quotation5. most favourable prices6. dispatch7. be given to understand that8. have confidence in9. moderate prices10. prom

22、ising market11. on the terms and conditions12. prompt attention13. by return14. owing to = on account of = because of15. business chance16. wholesalers17. retailers復習思考題、作業(yè)：Page No.29 Ex. II 課后小結(jié)： A general enquiry letter should be included in the followingparts :1 .the reason the letter2 .make a ge

23、neral enquiries by asking for catalogues price lists etc.3 .the closing sentence of the letterEnglish Business Correspondence 教案章 節(jié)：Chapter 2 Enquiry教學任務：Skill Training重點、難點：1. Making familiar with inquiry letters2. Expressions on making inquiries1. on the recommendation of2. come up to our expectat

24、ion3. regular orders4. with this in mind5. 川ustrated catalogueTraining Situations :Mr. Lawrence, General Manager of the United Textiles Company Ltd. (26 Lawton Street , Liverpool , England ), is a large dealer in textiles in England. He is interested in all of the Chinese silk products and now appro

25、aching China National Imp. & .Exp. Corp. , Shanghai Branch for a quotation for specific products. 將學生分為四組(進口商一出口商)進行詢盤信的實際案例操作，各 組推薦合格書信并做分析、講解，通過對照比較，大家講評選出優(yōu)秀 作品。目的通過案例分析，加強學生對詢盤信的深入了解，提高學生 的分析判斷能力，培養(yǎng)學生的實際應用能力。復習思考題、作業(yè)：Page No.29 Ex.III ; IV課后小結(jié)：要求學生熟練掌握詢盤信的撰寫及其慣用表達法。學生對具 體詢盤和一股詢盤的區(qū)別掌握得不錯，并能運用恰

26、當?shù)谋磉_法來撰寫詢盤信， 需要注意的是學生對個別詞匯的使用不當造成書信表達得不太流暢。例如English Business Correspondence 教案inqurie; inquiry; require; request章 節(jié)：Chapter Three Quotations & Offers教學目的：掌握報盤信函的翻譯和寫作內(nèi)容、方法、相關(guān)句型和詞匯。教學任務：Letter 1重點、難點：1 . The definition of an offer2 .The contents of an offer3 .How to judge a firm offer and a non-

27、firm offer1. The definition of an offer2. The meaning of a firm offer and a non-firm offer3. The three points of a firm offer4. confirm5. offer6. make sb. an offer for sth.7. European main ports8. firm9. subject to10. entertain11. counteroffer12. as regards13. under offer14. a large demand for15. ac

28、ceptance復習思考題、作業(yè)：Page .46 Ex. I13課后小結(jié)：熟練掌握實盤與虛盤的含義、實盤的三要素（清楚、完整和無 保留）、報盤信的撰寫及其慣用表達法。章 節(jié)：Chapter Three Quotations & Offer教學任務：Letter 2 Letter 6-1 Letter 6-2重點、難點：Making familiar with offering lettersExpressions on making offers1. at your request2. as requested3. on requested4. offer make sb.an of

29、fer for sth. Offer sb. sth.5. remain valid6. negotiation7. perfect combination of warmth, softness and easy care8. profitable business9. with thanks10. proforma invoice11. import licence12.there is no question about doing13.1 n compliance with1.1 in triplicate15 .meet with a favourable reception16 .

30、without delay復習思考題、作業(yè)：Page No. 47 Ex.IIEnglish Business Correspondence 教案課后小結(jié)：熟練掌握實盤與虛盤的區(qū)別、不同形式報盤信的撰寫及其慣用 表達法。章 節(jié)：Chapter Three Quotations & Offer教學任務：Skill Training重點、難,電：Making familiar with offering lettersExpressions on making offers教學內(nèi)容提要：根據(jù)以下提供的背景完成行文式和列表式報盤信的寫作：謝謝彳方1月12日的詢價?，F(xiàn)報盤如下，以你方十日內(nèi)復到

31、為條件：10公噸罐裝產(chǎn)筍，每罐£3.2倫敦到岸價，船期3/4月份。支付條款是憑即期 匯票支付的，保兌的，不可撤銷的信用證付款。相信上述報盤能為你方所接受。殷切期待好消息。將學生分為四組（進口商一出口商）進行報盤信的實際案例操作，各組推薦 合格書信并做分析、講解，通過對照比較，大家講評選出優(yōu)秀作品。目的通過 案例分析，加強學生對報盤信的深入了解，提高學生的分析判斷能力，培養(yǎng)學 生的實際應用能力。復習思考題、作業(yè)：Page No.47 Ex.I II; IV課后小結(jié)：1要求學生熟練掌握行文式的報盤信和列表式的報盤信的寫作及其慣用表達法。通過上述模擬實訓I,同學們對列表式報盤信的寫作明顯好

32、于 行文式，這是值得肯定的；但不容忽視的是必須要使學生明確對行文式的報盤 形式熟練掌握的重要性，這關(guān)系到口頭談判的勝算多少的問題。2要求學生明確實盤的三要素，尤其是對其中“交易條件的完整性”的規(guī)定涉及到對報盤有效期作出規(guī)定的重要性的理解。17章 節(jié)：Chapter Four Making Counter-offers & DecliningOrders教學目的：掌握還盤的翻譯和寫作方法、內(nèi)容、相關(guān)句型和詞匯。教學任務：Letter 1重點、難點： Making familiar with CounteroffersExpressions on making Counteroffers1

33、. on usual terms2. in reply.3. regret4. find5. out of line with6. indicate7. such being the case8. to be easily obtainable at a much lower figure9. to be prepared to do10.say, 10%11 .come to terms12 .at your earliest .convenience復習思考題、作業(yè)：Page No.61 Ex.I課后小結(jié)：要求學生熟練掌握婉言拒絕的表達法，學會在交易中如何拒絕 客戶的不合理要求并掌握原則：

34、 拒絕還盤或反還盤，并不意味著拒絕客戶。交 易不成有情在。切不可圖一時痛快而造成有損于買賣雙方貿(mào)易關(guān)系的事情。章 節(jié)：Chapter Four Making Counter-offers &Declining Orders教學任務：Letter 2 Letter 3重點、難點： Making familiar with CounteroffersExpressions on making Counteroffers1. be on the high side2. while3. appreciate your cooperation in doing sth4. be regretfu

35、l that5. reduce6. level7. be out of line with8. be firm with an upward tendency9. likelihood10.lapse11 .turn down12 .conclude the business with sb13 .take full advantage of the market14 .finalize the business with sb.15 .protracted exchange of correspondence16.sales contract復習思考題、作業(yè)：Page No.62 Ex. I

36、I要求學生熟練掌握婉言拒絕的表達法，學會在交易中如何拒絕客戶的還盤。English Business Correspondence 教案拒絕還盤信應具備以下內(nèi)容：1說明寫信原因；2拒絕還盤或反還盤；3說明 拒絕的理由；4說服對方接受原來的報盤；5分析市場行情意在敦促對方接受。章 節(jié)：Chapter Four Making Counter-offers &Declining Orders教學任務：Letter 5 Skill Training 重點、難點： Making familiar with CounteroffersExpressions on making Counteroff

37、ers教學內(nèi)容提要:1. shortage of stock2. the same3. undertake4. on account of5. uncertainty of raw materials6. revert7. feel free to do sth.8. rely on9. fresh order10. heavy commitments11. keep your inquiry before us將學生分為四組（進口商一出口商）進行還盤信、拒絕信的實際案例 操作，各組推薦合格書信并做分析、講解，通過對照比較，大家講評 選出優(yōu)秀作品。目的通過案例分析，加強學生對還盤信、拒絕信的深

38、 入了解，提高學生的分析判斷能力，培養(yǎng)學生的實際應用能力。復習思考題、作業(yè)：Page No.62 Ex. III課后小結(jié)：要求學生熟練掌握拒絕信的寫作技巧及相關(guān)的表達法。1.We regret to say that 2.We are regretful that 3 Much to our regret that19章 節(jié)：Chapter Five Acceptance & Orders教學目的：掌握成交信函的寫作、合同的翻譯和寫作、相關(guān)句型和詞匯。教學任務：Letter 1 Letter 2重點、難點： Making familiar with ordersExpressions

39、on conclusion of orders1. confirm have done the business with sb.2. through your full cooperation3. revised price4. purchase confirmation5. for our file6. be in urgent need of7. make punctual shipment8. delay in shipment9. detrimental to10. to find a good market for11. a high demand12. conclude an o

40、rder with sb.13. sales confirmation14 .make15 .repeat orders復習思考題、作業(yè)：Page No.76 Ex.I課后小結(jié)：1.要求學生明確有效接受的四個標志；2.熟練掌握接受的表達 法和接受信、訂貨信及簽訂合同信的寫作技巧。章 節(jié)：Chapter Five Acceptance & Orders教學任務：Letter 5重點、難點： Making familiar with ordersExpressions on conclusion of orders教學內(nèi)容提要：1. confirm have done the busine

41、ss with sb.2. through your full cooperation3. revised price4. purchase confirmation5. for our file6. be in urgent need of7. make punctual shipment8. delay in shipment9. detrimental to10. to find a good market for11. 11.a high demand12. conclude an order with sb.13. sales confirmation14. make15. repe

42、at orders復習思考題、作業(yè)：Page No.76 Ex.II課后小結(jié)：熟練掌握接受的表達法和接受信、訂貨信及簽訂合同信的寫作 技巧。明確什么是說明信及撰寫說明信的要點。English Business Correspondence 教案章 節(jié)：Chapter Five Acceptance & Orders教學任務：Skill TrainingSales Contract / ConfirmationPurchase Contract / Confirmation重點、難點： The contents of a contractHow to fill in contract1.

43、 contract No.2. Sellers/Buyers3. Commodity4. Specifications5. Quantity6. Unit Price7. Total Value8. Shipping Mark9. Insurance10. Time of Shipment11. Port of Shipment & Destination12. Terms of Payment13. Packing14.Signing place & Date復習思考題、作業(yè)：Page No.78 Ex. III課后小結(jié)：熟練掌握合同的基本內(nèi)容以及用英文填寫合同的基本方法。章

44、 節(jié)：Chapter Five Acceptance & Orders教學任務：Skill Training重點、難點： Making familiar with ordersExpressions on conclusion of orders教學內(nèi)容提要：根據(jù)以下提供的背景完成行文式和列表式訂貨信的寫作：茲高興地確認按照下列條款賣給你方 29英寸東芝彩色電視機2000臺：2000臺29英寸東芝彩色電視機，橫濱成本、保險家運費價每臺美元，木箱裝，每箱裝4臺。收到信用證一周內(nèi)，從橫濱運至大連。請?zhí)貏e注意貨物的包裝，以免貨物在運輸途中受損。我們現(xiàn)在正在洽辦開信用證，在接到你方確認書后，即

45、可開出以你方為受益 人的信用證。將學生分為四組（進口商一出口商）進行接受信、訂貨信的實際案例操作， 各組推薦合格書信并做分析、講解，通過對照比較，大家講評選出優(yōu)秀作品。 目的通過案例分析，加強學生對接受信、訂貨信的深入了解，提高學生的分析 判斷能力，培養(yǎng)學生的實際應用能力。復習思考題、作業(yè)：Page No. 78 Ex.IV 課后小結(jié)：熟練掌握接受的表達法和接受信及簽訂合同信的寫作技巧。熟練掌握行文式和列表式訂貨信的寫作方法。注意accept; acceptance ; confirmhaving done sth 的區(qū)別使用。29章 節(jié)：Chapter Six Terms of Paymen

46、t教學目的：掌握與支付條款有關(guān)的各類信函的翻譯和寫作、相關(guān)句型和詞匯。教學任務：Letter 1 Letter 2重點、難點：I.The Mode of Payment2 .The relationship between business letters3 .The useful expressions on Payment1. pay2. .to pay in advance3. to pay by instalmentsa) to pay on deliveryb) to pay by 30 days L/Cc) to pay by time L/C at 30 days4. invol

47、ve =5. means6. at hand7. tie-up of funds = tying up funds8. extend = accord , give9. accommodation復習思考題、作業(yè)： 1 What are the modes of payment in international trade?2 What is D/P? What is D/A?課后小結(jié)：要求學生明確支付在國際貿(mào)易中的重要作用，了解國 際貿(mào)易中常用的支付方式以及用英語表述的方法。章 節(jié)：Chapter Six Terms of Payment教學任務：Letter 3 Letter 4 Lett

48、er 5重點、難點： Making familiar with the mode of paymentExpressions on payment terms教學內(nèi)容提要：1. nothing unusual2. arrangement3. in addition4. the goods are ready for shipment5. adhere to6. usual practice7. affect8. in the amount of9. for the amount of10. to the amount of11. in value12. CAD13. meet with you

49、r approval14. make it clear that15. direct payment16. equivalent in RMB17. figure18. exception19. in the light of復習思考題、作業(yè)：Page No.96 Ex.課后小結(jié)：熟練掌握國際貿(mào)易結(jié)算方式.支付信的撰寫及其慣用表達法章節(jié)：Chapter Six Terms of Payment教學任務：Skill Training 重點、難點： Making familiar with the mode of paymentExpressions on payment terms教學內(nèi)容提要：

50、根據(jù)以下提供的背景完成支付信的寫作:1 .十一月十二日來函收到，獲悉你方有意在貴國推銷我們的自行車。對此， 我們非常感興趣。2 .對你方為推銷自行車所做的努力我們甚為感激。3 .但對你方要求以見票后六十天承兌交單方式付款一事，我們歉難考慮。4 .我們的通常做法是要求即期信用證付款。5 .為了促進我方自行車在貴方市場上的銷售， 我方準備接受即期付款交單方 式，以示特別照顧。希望你方能接受上述付款條件并盼早日收到回音。將學生分為四組（進口商一出口商）進行支付信的實際案例操作，各組推薦合 格書信并做分析、講解，通過對照比較，大家講評選出優(yōu)秀作品。目的通過案 例分析，加強學生對支付信的深入了解，提高學

51、生的分析判斷能力，培養(yǎng)學生 的實際應用能力。復習思考題、作業(yè)：Page No. 97 Ex. II課后小結(jié)：要求學生熟練掌握國際貿(mào)易結(jié)算方式.支付信的撰寫及其慣 用表達法。章 節(jié)：Chapter Seven Letter of Credit教學目的：掌握信用證的開立和修改信函寫作、相關(guān)句型和詞匯。教學任務：Letter 1 Letter 2重點、難點：1. The basic contents of an L/C2.Advising the opening of an L/C1. expire2. delay in doing sth3. applicant4. beneficiary5. a

52、dvising bank6. negotiating bank7. paying bank8. notifying bank9. issuing bank10. on examination11. direct steamer12. partial shipment13. more often than not14. infrequent15. speed matter up16. amend復習思考題、作業(yè)：Page No.112 Ex.I課后小結(jié)：要求學生明確信用證的基本內(nèi)容、當事人；信用證的 性質(zhì)以及用信用證支付的基本程序。章 節(jié)：Chapter Seven Letter of Cred

53、it教學任務：Letter 6重點、難點：1. Checking an L/C2. The basic contents of checking an L/C3. Amendment to the L/C1 .the nature & terms of the L/C must be exact accordance with S/C1. the names of parties concerned2. the number of the L/C3. the amount of the L/C4. Is it sight L/C or term L/C5. the expiration

54、 of the L/C6. shipment terms8.on the part of suppliers9 .to that effect10 .consignment11.in the early part of12.S.S "Blue Seas13.effect shipment4.discrepancy復習思考題、作業(yè)：Page No.112 Ex.II課后小結(jié)：要求學生熟練掌握審核信用證的基本要點及如何審證 并能寫出一封要求買方修改信用證的書信。章 節(jié)：Chapter Seven Letter of Credit教學任務：Letter 4 Letter 5 Letter

55、3 Letter 7重點、難點：1. Extension of an L/C2. Urging establishing an L/C學內(nèi)容提要：1. on the part of2. get the shipment ready3. consignment4. to that effect5. in the early part of6. unduly inconvenience7. abide by8. expedite9. execute the order10. due to11. be in strict conformity with12. match13. ensure14. e

56、xtend15. amendment notice復習思考題、作業(yè)：Page No.114 Ex.III課后小結(jié)：要求學生掌握催證信、展證信的寫作技巧及慣用表達 方式。章 節(jié)：Chapter Seven Letter of Credit教學任務：Skill Training重點、難點：掌握信用證的基本內(nèi)容依據(jù)合同內(nèi)容來審核信用證及其基本步驟依據(jù)提供的背景完成催證信、展證信的寫作教學內(nèi)容提要：依據(jù)提供的背景完成審核信用證并寫出改證信：將要求改證的信函示例展示給學生，根據(jù)所掌握的信用證的審核內(nèi) 容進行實際案例操作，通過討論大家推薦合格書信并做分析、 講解, 通過對照比較，大家講評選出優(yōu)秀作品。目的通過案例分析，加強 學生對信用證審證和改證的深入了解，提高學生