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人教A版高中数学必修二空间点、直线、平面之间的位置关系教学设计
9.例二：如图，AB∩α=B,A?α， ?a.直线AB与a具有怎样的位置关系？为什么？解：直线AB与a是异面直线。理由如下：若直线AB与a不是异面直线，则它们相交或平行，设它们确定的平面为β，则B∈β， 由于经过点B与直线a有且仅有一个平面α，因此平面平面α与β重合，从而 , 进而A∈α，这与A?α矛盾。所以直线AB与a是异面直线。补充说明：例二告诉我们一种判断异面直线的方法：与一个平面相交的直线和这个平面内不经过交点的直线是异面直线。10. 例3 已知a，b，c是三条直线，如果a与b是异面直线，b与c是异面直线，那么a与c有怎样的位置关系？并画图说明．解： 直线a与直线c的位置关系可以是平行、相交、异面．如图(1)(2)(3)．总结：判定两条直线是异面直线的方法(1)定义法：由定义判断两条直线不可能在同一平面内．
中 央 空 调 采 购 及 安 装 合 同
根据《中华人民共和国合同法》等有关法律、法规、规章、部门及行业规定、标准等的规定，并结合本工程具体情况，遵循平等、自愿、公平和诚实信用的原则，甲乙双方经友好协商，签订本合同。1.产品数量、价格1.1产品清单：序号 设备名称 型号和规格 产地 单位 数量 单价(万元) 总价（万元） 备注1 2 3 4 设备安装费 5 总计（大写）：甲方采购乙方经销的 型号中央空调 台，合同总价: 人民币 ，详细价格见下表：1.2 该价格为固定价格，在合同有效期内，甲方不承担因各种因素所导致的成本上升而产生的价格上涨风险。1.3该价格中包括设备生产、包装、保险、运输、装卸、安装、调试（包括配合调试）及验收合格之前及保修期内备品备件发生的含税费用。1.4 专利：乙方必须保障甲方在使用其提供的产品时不受到第三方关于侵犯专利权、商标权、外观设计或工业设计权等知识产权的指控。任何第三方如果提出侵权指控，乙方必须与第三方交涉并承担可能发生的一切法律和费用责任。如因乙方原因，甲方收到政府职能部门或第三方合法追诉或指控的，造成的所有损失由乙方承担，包括但不限于处理此事所生的律师代理费用。
鲜蛋购销合同
根据《中华人民共和国合同法》等有关法律的规定，经双方协商，签订本合同，共同信守，严格履行。第一条 品名、计量单位、数量第二条 产品质量与标准：供方出售给需方的鲜蛋应新鲜完整、不破损、不变质，保持鲜蛋表面清洁，不沾附泥污等物。第三条 包装要求：由自备或向需方租用硬塑箱及木箱，由供方付给需方押金与使用费。第四条 价格或作价办法：全年实行季节差价。收购旺季实行量低保护价，鸡蛋每市斤 元，补贴饲料 斤；鸭蛋每市斤 元，补贴饲料 斤。第五条 收购地点： 。第六条 交货方式及运费负担：供方鲜蛋送往需方仓库，必须自备车辆、船只或其他运输工具。需方收货后则应按实际数量，每百斤补贴运输费、损耗 元，交食品站不补贴运杂费及损耗。第七条 验收方式与期限：供方将鲜蛋送到后，需方依次过磅照验，在24小时内验收完毕，逾期验收由需方补贴损耗 ％。
XX年秋季开学第一周国旗下讲话稿：《新学期 新气象》
XX年秋季开学第一周国旗下讲话稿：《新学期新气象》老师们、同学们：大家好！今天我国旗下演讲的题目是《新学期新气象》新学期，对于我们每个人来说都将开启新的希望，承载新的梦想。站在新的起点上，大家是否已整装待发，准备好踏上新的征程？无论是踌躇满志，心中向往一片天地；还是厚积薄发，立志成为一匹黑马，相信各位定是胸怀大志，心有不凡。而即将开启的旅程，将是证明我们自身的最好机会！高一的同学们，你们若是怀揣梦想，一中便会是你圆梦的舞台，但没有什么成功是一蹴而就的。俗话说，良好的开端等于成功的一半。立下目标，并将自己最大的热情投身其中。要惜时，专心，善思，脚踏实地，一步一个脚印，夯实基础，适当拔高。兵家云：“知己知彼，百战不殆。”相信你们一定能尽快融入到一中优秀的学习环境中并更加优秀！高二的同学们，我们已经褪去了高一时的青涩，更加理智，更加成熟。高二是最关键的一年，也是最容易被忽视的一年。要时刻提醒自己，离最终的华山论剑已不再遥远。
月是故乡明（说课稿）
一、教材分析：《月是故乡明》是散文大家季羡林老先生的散文名篇，作于78岁高龄。文章以月作为抒情线索，通过对故乡和自己童年生活的回忆，特别是对故乡月色的动人描写，抒发了作者对故乡永远的思念与牵挂。文章语言古拙、质朴，但越是这样的质朴自然，越是能见出作者对故乡的至情至爱。“真”与“朴”也正是季先生散文的两大特点和独特风格。同时散文“形散而神不散”的特点在本文中也表现得很充分。根据以上教材特点和新课标理念以及学生的实际情况，我确立以下教学目标： 二、教学目标1.知识与能力：体会散文形神的辩证关系；掌握阅读散文的基本方法；培养学生鉴赏散文的能力2.过程与方法：学习并掌握抒情散文的写作特点；训练学生运用语言文字的能力； 3.情感态度与价值观：引导学生体会作品表现的人对家园和故乡的刻骨铭心的依恋之情及其深刻内涵；进一步认识故乡对一个人成长的重要意义，激发对家乡的热爱之情。
《故宫博物院》说课稿
说教学目标：? 1.了解故宫博物院建筑群规模宏大、建筑精美、布局统一的特点。?2.了解方位词在空间说明顺序中的重要作用。?3.能画出故宫的路线图，并选择其中一两个景点进行讲解。?4.增强学生的民族自豪感，进一步激发他们民族创造精神。三、说教学重难点：1.了解故宫博物院建筑群规模宏大、建筑精美、布局统一的特点。?2.认真阅读课文，了解故宫建筑群的宏伟壮丽，学习按空间顺序说明事物的方法。3.体会本文重点突出，有详有略的说明事物的写法，学以致用。四、说教学方法：? 根据新课标中“从实际出发，遵循知识传授与能力发展相结合，形象感知与逻辑思维相结合，性情陶冶与知识拓展相结合以及以学生本位”的原则，本节课所使用的主要教学方法有：1.讨论法和点拨法结合。设计相关问题指导学生阅读，提醒学生注意方位词的。在老师的点拨下，帮助学生理清文章的说明顺序。
新人教版高中英语必修3Unit 1 Festivals and Celebrations教学设计三
*wide range of origins(= a great number of different origins, many kinds of origins)*It featured a parade and a great feast with music, dancing, and sports. (=A parade and a great feast with music, dancing, and sports were included as important parts of the Egyptian harvest festival.)*.. some traditions may fade away and others may be established.(= Some traditions may disappear gradually, while other new traditions may come into being.）Step 6 Practice(1) Listen and follow the tape.The teacher may remind the students to pay attention to the meaning and usage of the black words in the context, so as to prepare for the completion of the blanks in activity 5 and vocabulary exercises in the exercise book.(2) Students complete the text of activity 5 by themselves.The teacher needs to remind the students to fill in the blanks with the correct form of the vocabulary they have learned in the text.Students exchange their answers with their partners, and then teachers and students check their answers.(3)Finish the Ex in Activity 5 of students’ book.Step 7 Homework1. Read the text again, in-depth understanding of the text;2. Discuss the origin of festivals, the historical changes of related customs, the influence of commercial society on festivals and the connotation and essential meaning of festivals.3. Complete relevant exercises in the guide plan.1、通过本节内容学习，学生是否理解和掌握阅读文本中的新词汇的意义与用法；2、通过本节内容学习，学生能否结合文本特点快速而准确地找到主题句；3、通过本节内容学习，学生能否理清论说文的语篇结构和文本逻辑，了解节日风俗发展与变迁，感悟节日的内涵与意义。
新人教版高中英语必修3Unit 2 Morals and virtues教学设计一
(2) students are divided into groups according to the requirements of activity 3. Each student shares a story of personal experience or hearing-witnessing kindness, and then selects the most touching story in the group and shares it with the whole class. Before the students share the story, the teacher can instruct them to use the words and sentence patterns in the box to express. For example, the words in the box can be classified:Time order: first of all, then, after that, later, finally logical relationship :so, however, although, butTeachers can also appropriately add some transitional language to enrich students' expression:Afterwards, afterwards, at last, in the end, eventuallySpatial order: next to, far from, on the left, in front ofOtherwise, nevertheless, as a result, therefore, furthermore, in addition, as well asSummary: in a word, in short, on the whole, to sum up, in briefStep 8 Homework1. Understand the definition of "moral dilemma" and establish a correct moral view;2. Accumulate vocabulary about attitudes and emotions in listening texts and use them to express your own views;3. Complete relevant exercises in the guide plan.1、通过本节内容学习，学生能否理解理解“道德困境”的定义；2、通过本节内容学习，学生能否通过说话人所表达的内容、说话的语气、语调等来判断其态度和情绪；3、通过本节内容学习，学生能否针对具体的道德困境发表自己的看法和见解，能否掌握听力理训练中的听力策略。
新人教版高中英语选修2Unit 4 Reading and thinking教学设计
【词汇精讲】highlight n.最好或最精彩的部分 vt.突出;强调;使醒目One of the highlights of the trip was seeing the Taj Mahal.这次旅行的亮点之一是参观泰姬陵。Your resume should highlight your skills and achievements.你的简历应该突出你的技能和成就。The report highlights the major problems facing society today.报告强调了当今社会所面临的主要问题。I’ve highlighted the important passages in yellow.我用黄色标出了重要段落。7.Edmonton is freezing cold in winter,with daily temperatures averaging -10 ℃.埃德蒙顿冬季寒冷,日平均气温为-10°C。【词汇精讲】freezing adj.极冷的;冰冻的Leave a basin of water outside in freezing weather.在冰冻的天气里,放一盆水在室外。It’s freezing cold outside so wear a warm coat.外面超冷的,所以穿一个暖和一点的外套吧。8.It was not until 9:30 a.m.that they finally reached the capital of Ontario,Toronto.直到上午9时30分,他们才终于到达多伦多的首府安大略省。【句式剖析】本句是一个强调句,强调的是句子的时间状语until 9:30。含有not...until...的句子的强调句为It is not until...that...,that后面的句子要用肯定形式。It was not until then that I suddenly realized nobody was happier than I was.直到那时我才突然意识到没有人比我更幸福了。
新人教版高中英语选修2Unit 5 Reading for writing教学设计
你校英语报计划出版一期急救常识专刊,现面向全校学生公开征集稿件,你有意参加。请你根据下面提示内容,用英语写一篇短文,介绍在车祸现场对伤者进行急救的方法和步骤。1.确保现场的安全;2.询问伤者,确保其呼吸正常;3.检查伤口,如流血则应采取止血措施;4.如需急救,确保其处于康复位置。注意:1.词数80左右;2.可以适当增加细节,以使行文连贯。参考词汇:康复位置 recovery positionAs we all know, having a knowledge of first aid can make a great difference in our daily life. If a traffic accident happens and someone is injured, the following steps can be used to treat the injured.In the first place, we should make sure that the accident scene is safe so that we won’t get hurt. We should ask the injured person if he is OK, and see if he is breathing. What’s more, we should check for cuts and wounds. If he is bleeding badly, it is vital that we should try to stop the bleeding by applying pressure to the injury. This is because if a person loses too much blood, he may die. If necessary, take the injured person to the hospital as soon as possible.Do remember: when giving first aid, please be sure to place the person in a recovery position.
新人教版高中英语选修2Unit 3 Reading for writing教学设计
The theme of this part is to write an article about healthy diet. Through reading and writing activities, students can accumulate knowledge about healthy diet, deepen their understanding of the theme of healthy diet, and reflect on their own eating habits. This text describes the basic principles of healthy diet. The author uses data analysis, definition, comparison, examples and other methods. It also provides a demonstration of the use of conjunctions, which provides important information reference for students to complete the next collaborative task, writing skills, vivid language materials and expressions.1. Teach Ss to learn and skillfully use the new words learned from the text.2. Develop students’ ability to understand, extract and summarize information.3. Guide students to understand the theme of healthy diet and reflect on their own eating habits.4. To guide students to analyze and understand the reading discourse from the aspects of theme content, writing structure, language expression, etc., 5. Enable Ss to write in combination with relevant topics and opinions, and to talk about their eating habits.1. Guide students to analyze and understand the reading discourse from the aspects of theme content, writing structure, language expression, etc.2. Enable them to write in combination with relevant topics and opinions, and to talk about their eating habits.3. Guide the students to use the cohesive words correctly, strengthen the textual cohesion, and make the expression fluent and the thinking clear.Step1: Warming upbrainstorm some healthy eating habits.1.Eat slowly.2.Don’t eat too much fat or sugar.3.Eat healthy food.4.Have a balanced diet.Step2: Read the passage and then sum up the main idea of each paragraph.
新人教版高中英语选修2Unit 2 Using langauge-Listening教学设计
? B: Absolutely! Getting involved with Chinese cultural activities there definitely helped a lot. I got to practice my Chinese on a daily basis, and I could learn how native Chinese speakers spoke.? A: What do you feel is your biggest achievement?? B: Learning Chinese characters! I have learnt about 1,500 so far. When I first started, I didn't think it was even going to be possible to learn so many, but now I find that I can read signs, menus, and even some easy newspaper articles.? A: What are you most keen on?? B: I've really become keen on learning more about the Chinese culture, in particular Chinese calligraphy. As I have learnt Chinese characters, I have developed a great appreciation for their meaning. I want to explore Chinese characters by learning how to write them in a more beautiful way. ? A: Finally, what do you want to say to anyone interested in learning Chinese?? I have really become keen on learning more about the Chinese culture, in particular Chinese Calligraphy. As I have learnt Chinese character, I have developed a great appreciation for their meaning. I want to explore Chinese characters by learning how to write them in a more beautiful way.? A: Finally, what do you want to say to anyone interested in learning Chinese?? B: I'd say, give it a shot! While some aspects may be difficult, it is quite rewarding and you will be happy that you tried.? A: Thanks for your time. ? B:You're welcome.
新人教版高中英语选修2Unit 4 Reading for writing教学设计
假定你是英国的Jack，打算来中国旅行，请你给你的中国笔友李华写一封信，要点如下：1．你的旅行计划：北京→泰山→杭州；2．征求建议并询问他是否愿意充当你的导游。注意：1.词数80左右(开头和结尾已给出，不计入总词数)；2．可以适当增加细节，以使行文连贯。参考词汇：故宫 the Forbidden City；泰山 Mount TaiDear Li Hua，I'm glad to tell you that 'm going to visit China.First，I am planning to visit Beijing，the capitalof China，where I am looking forward to enjoying the Great Wall，the Forbidden City and somebeautiful parks.Then I intend to go to visit Mount Tai in Shandong Province.I've heard that it is one ofthe most famous mountains in China and I can't wait to enjoy the amazing sunrise there.After that，I amalso going to Hangzhou.It is said that it is a beautiful modern city with breathtaking natural sights，among which the West Lake is a well- known tourist attraction.What do you think of my travel plan? Will you act as my guide? Hope to hear from you soon.
新人教版高中英语选修2Unit 5 Reading and thinking教学设计
The theme of this activity is to learn the first aid knowledge of burns. Burns is common in life, but there are some misunderstandings in manual treatment. This activity provides students with correct first aid methods, so as not to take them for granted in an emergency. This section guides students to analyze the causes of scald and help students avoid such things. From the perspective of text structure and collaborative features, the text is expository. Expository, with explanation as the main way of expression, transmits knowledge and information to readers by analyzing concepts and elaborating examples. This text arranges the information in logical order, clearly presents three parts of the content through the subtitle, accurately describes the causes, types, characteristics and first aid measures of burns, and some paragraphs use topic sentences to summarize the main idea, and the level is very clear.1. Guide students to understand the causes, types, characteristics and first aid methods of burns, through reading2. Enhance students’ ability to deal withburnss and their awareness of burns prevention3. Enable students to improve the ability to judge the types of texts accurately and to master the characteristics and writing techniques of expository texts.Guide students to understand the causes, types, characteristics and first aid methods of burns, through readingStep1: Lead in by discussing the related topic:1. What first-aid techniques do you know of ?CPR; mouth to mouth artificial respiration; the Heimlich Manoeuvre
新人教版高中英语必修3Unit 1 Festivals and Celebrations教学设计二
1. Ss look at the picture and scan the passage to understand the main idea while teacher is giving the following questions to inspire Ss to think.*Where are those people?*What are they doing?*Why are they so excited?2. Ss complete the passage with the appropriate -ing form. Then discuss and check the answers with class.Answers: boring, interesting, taking, exciting, amazing3. The teacher raises questions for the students to discuss and encourages them to express their opinions.*Do you like La Tomatina? Why or why not?4. Each group representative reports the discussion result, the teacher gives feedback and the evaluation.Step 6 PracticeActivity 41. Ss complete the Ex 2 in Using structures.2. Check the answers after finishing the exercises.①The dragon boat races are the most exciting part of the Dragon Boat Festival.② The children were excited to go Easter egg hunting.③What an amazing performance! This is the best music festival I have ever been to.④We were amazed by her funny-looking hat.⑤His inspiring speech at the conference won the admiration/ favour of the audience.⑥This is a challenging game to test your memory and observation capabilities. 3. T asks Ss to finish Ex 3 and 4 in Using structures by themselves, then check the answers with class.Step 6 Homework1. Understand and master the functions and usage of the -ing form;2. Finish the other exercises in Using structures.1、通过本节内容学习，学生是否理解和掌握动词-ing形式作定语和表语的功能和意义；2、通过本节内容学习，学生能否在理解文段内容的基础上，根据上下文语境和表达逻辑，能正确运用动词-ing形式描述节日庆典。3、通过本节内容学习，学生是否归纳和积累用于表达情绪的相关词汇。
新人教版高中英语必修3Unit 1 Festivals and Celebrations教学设计一
本板块的活动主题是“谈论节日活动”（Talk about festival activities），主要是从贴近学生日常生活的角度来切入“节日”主题。学生会听到发生在三个国家不同节日场景下的简短对话，对话中的人们正在参与或将要亲历不同的庆祝活动。随着全球化的进程加速，国际交流日益频繁，无论是国人走出国门还是外国友人访问中国，都已成为司空见惯的事情。因此，该板块所选取的三个典型节日场景都是属于跨文化交际语境，不仅每组对话中的人物来自不同的文化背景，对话者的身份和关系也不尽相同。1. Master the new words related to holiday: the lantern, Carnival, costume, dress(sb)up, march, congratulation, congratulate, riddle, ceremony, samba, make - up, after all. 2. To understand the origin of major world festivals and the activities held to celebrate them and the significance of these activities;3. Improve listening comprehension and oral expression of the topic by listening and talking about traditional festivals around the world;4. Improve my understanding of the topic by watching pictures and videos about different traditional festivals around the world;5. Review the common assimilation phenomenon in English phonetics, can distinguish the assimilated phonemes in the natural language flow, and consciously use the assimilation skill in oral expression. Importance:1. Guide students to pay attention to the attitude of the speaker in the process of listening, and identify the relationship between the characters;2. Inspire students to use topic words to describe the festival activities based on their background knowledge. Difficulties:In the process of listening to the correct understanding of the speaker's attitude, accurately identify the relationship between the characters.
新人教版高中英语必修3Unit 2 Morals and Virtues教学设计二
Activity 41. Students complete the task of activity 4, then teachers and students check the answers. 2. The teacher organized the students to work together and asked them to use the tables and mind maps sorted out before to retold the important choices in Lin Qiaozhi's life and their resultsStep 5 Language points1. The teacher asks the students to read the text carefully, find out the core words and long and difficult sentences in the text and draw lines, understand the use of vocabulary, and analyze the structure of long and difficult sentences. 2. The teacher explains and summarizes the usage of core vocabulary and asks the students to take notes. 3. The teacher analyzes and explains the long and difficult sentences that the students don't understand, so that the students can understand them better. Step 6 Homework1. Read the text again, in-depth understanding of the text; 2. Master the use of core vocabulary and understand the long and difficult sentences. 3. Complete relevant exercises in the guide plan. 1、通过本节内容学习，学生是否理解和掌握阅读文本中的新词汇的意义与用法；2、通过本节内容学习，学生能否结合文本特点总结林巧稚的人生原则和人格品质特征；3、通过本节内容学习，学生能否针对人生抉择发表自己的看法；能否全面地、客观地、理性地看待问题，进而对道德和人性有更加深入的思考和理解。
新人教版高中英语必修3Unit 2 Morals and Virtues教学设计三
The joke set her crying.这个玩笑使她哭起来。Step 5 ReadingActivity 31. Students read the small text in activity 3. The teacher provides several small questions to check whether students understand the content of the text and the ideographic function of the -ing form in the text.*Where are those people?*Why did Dr Bethune come to China?*How did he help the Chinese people during the war?*What did Chairman Mao Zedong say about him?2. Ss try to rewrite some sentences using the -ing form. Then check the answers. When checking the answers, the teacher can ask different students to read the rewritten sentences and give comments.Answers:1. he became very interested in medicine, deciding to become a doctor.2. …after hearing that many people were dying in the war.3. Helping to organise hospitals, he taught doctors and nurses, and showed people how to give first aid./ He helped to organise hospitals, teaching doctors and nurses, and showing people how to give first aid.4. …praising Dr Bethune as a hero to be remembered in China.Step 6 PracticeActivity 4Students complete grammar activities 2 and 3 on page 69 of the workbook.Step 6 Homework1. Understand and master the functions and usage of the -ing form;2. Finish the other exercises in Using structures.1、通过本节内容学习，学生是否理解和掌握动词-ing形式作宾语补足语语和状语语的功能和意义；2、通过本节内容学习，学生能否正确使用动词-ing形式描述人物的行为、动作及其经历；3、通过本节内容学习，学生能否独立完成练习册和导学案中的相关练习。
新人教版高中英语必修3Unit 2 Morals and Virtues教学设计四
3.Teachers ask different groups to report the answers to the questions and ask them to try different sentence patterns.The teacher added some sentence patterns for students to refer to when writing.Step 4 Writing taskActivity 51.Write the first draft.Students first review the evaluation criteria in activity 5, and then independently complete the draft according to the outline of activity 4, the answers to the questions listed in the group discussion and report, and the reference sentence pattern.2.Change partners.The teacher guides the students to evaluate their partner's composition according to the checklist of activity 5 and proposes Suggestions for modification.3.Finalize the draft.Based on the peer evaluation, students revise their own compositions and determine the final draft.Finally, through group recommendation, the teacher selects excellent compositions for projection display or reading aloud in class, and gives comments and Suggestions.Step 5 Showing writingActivity 5T call some Ss to share their writing.Step 6 Homework1. Read the passage in this section to better understand the passage.2. Carefully understand the hierarchical structure of the article, and deeply understand the plot of the story according to the causes, process and results;3. Independently complete the relevant exercises in the guide plan.1、通过本节内容学习，学生是否理解和掌握阅读文本中的新词汇的意义与用法；2、通过本节内容学习，学生能否通过人物言行的对比分析道德故事的深层内涵；3、通过本节内容学习，学生能否根据故事的起因、经过和结果来深入理解故事的情节，从而了解文章的层次结构；4、结合现实生活案例发表自己的见解和看法,写一篇观点明确、层次分明的故事评论。
新人教版高中英语必修3Unit 3 Diverse Cultures教学设计三
The price is the same as(the price was)before the war.价格与战前相同。(4)定语从句中的“关系代词＋助动词be”可以省略。The ticket(that/which was)booked by his sister has been sent to him.他妹妹订的那张票已送到了他那里。Step 5 PracticeActivity 3(1) Guide students to complete the four activities in the Using Structures part of exercise book, in which activities 1 and 2 focus on ellipsis in dialogue answers, activity 3 focus on signs and headlines, two typical situations where ellipsis is used, and activity 4 focus on ellipsis in diary, an informal style.(2) Combine the examples in the above activities, ask students to summarize the omitted situations in groups, and make their own summary into a poster, and post it on the class wall after class to share with the class.(This step should give full play to the subjectivity of students, and teachers should encourage students to conclude different ellipsis phenomena according to their own understanding, they can conclude according to the different parts omitted in the sentence.)Step 6 Homework1. Understand and master the usages of ellipsis;2. Finish the other exercises in Using structures of Workbook.1、通过本节内容学习，学生是否理解和掌握省略的用法；2、通过本节内容学习，学生能否根据上下文语境或情景恢复句子中省略的成分，体会使用省略的效果；3、通过本节内容学习，学生能否独立完成练习册和导学案中的相关练习。
