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人教版高中数学选择性必修二等比数列的前n项和公式 (2) 教学设计
二、典例解析例10. 如图，正方形ABCD 的边长为5cm ，取正方形ABCD 各边的中点E,F,G,H, 作第2个正方形 EFGH，然后再取正方形EFGH各边的中点I,J,K,L，作第3个正方形IJKL ，依此方法一直继续下去. (1) 求从正方形ABCD 开始，连续10个正方形的面积之和；(2) 如果这个作图过程可以一直继续下去，那么所有这些正方形的面积之和将趋近于多少？分析：可以利用数列表示各正方形的面积，根据条件可知，这是一个等比数列。解：设正方形的面积为a_1，后续各正方形的面积依次为a_2, a_(3, ) 〖…,a〗_n,…，则a_1=25,由于第k+1个正方形的顶点分别是第k个正方形各边的中点，所以a_(k+1)=〖1/2 a〗_k,因此{a_n}，是以25为首项，1/2为公比的等比数列.设{a_n}的前项和为S_n（1）S_10=(25×[1-(1/2)^10 ] )/("1 " -1/2)=50×[1-(1/2)^10 ]=25575/512所以，前10个正方形的面积之和为25575/512cm^2.(2)当无限增大时，无限趋近于所有正方形的面积和
人教版高中数学选择性必修二等差数列的前n项和公式（2）教学设计
课前小测1．思考辨析(1)若Sn为等差数列{an}的前n项和，则数列Snn也是等差数列．( )(2)若a1>0，d<0，则等差数列中所有正项之和最大．( )(3)在等差数列中，Sn是其前n项和，则有S2n－1＝(2n－1)an.( )[答案] (1)√ (2)√ (3)√2．在项数为2n＋1的等差数列中，所有奇数项的和为165，所有偶数项的和为150，则n等于( )A．9 B．10 C．11 D．12B [∵S奇S偶＝n＋1n，∴165150＝n＋1n.∴n＝10.故选B项．]3．等差数列{an}中，S2＝4，S4＝9，则S6＝________.15 [由S2，S4－S2，S6－S4成等差数列得2(S4－S2)＝S2＋(S6－S4)解得S6＝15.]4．已知数列{an}的通项公式是an＝2n－48，则Sn取得最小值时，n为________.23或24 [由an≤0即2n－48≤0得n≤24.∴所有负项的和最小，即n＝23或24.]二、典例解析例8.某校新建一个报告厅，要求容纳800个座位，报告厅共有20排座位，从第2排起后一排都比前一排多两个座位. 问第1排应安排多少个座位？分析：将第1排到第20排的座位数依次排成一列，构成数列{an} ，设数列{an} 的前n项和为S_n。
人教版高中数学选择性必修二等差数列的前n项和公式（1）教学设计
高斯（Gauss，1777－1855），德国数学家，近代数学的奠基者之一. 他在天文学、大地测量学、磁学、光学等领域都做出过杰出贡献. 问题1：为什么1＋100＝2＋99＝…＝50＋51呢？这是巧合吗？试从数列角度给出解释.高斯的算法：（1+100）+（2+99）+…+(50+51)= 101×50=5050高斯的算法实际上解决了求等差数列：1，2，3，…，n，"… " 前100项的和问题.等差数列中，下标和相等的两项和相等.设 an＝n，则 a1＝1，a2＝2，a3＝3，…如果数列{an} 是等差数列，p，q，s，t∈N*，且 p＋q＝s＋t，则 ap＋aq＝as＋at 可得：a_1+a_100=a_2+a_99=?=a_50+a_51问题2： 你能用上述方法计算1＋2＋3＋… ＋101吗？问题3： 你能计算1＋2＋3＋… ＋n吗？需要对项数的奇偶进行分类讨论.当n为偶数时， S_n=(1+n)+[(2+(n-1)]+?+[(n/2+(n/2-1)]=(1+n)+(1+n)…+(1+n)=n/2 (1+n) =(n(1+n))/2当n为奇数数时， n－1为偶数
人教版高中数学选择性必修二等差数列的概念（1）教学设计
我们知道数列是一种特殊的函数，在函数的研究中，我们在理解了函数的一般概念，了解了函数变化规律的研究内容（如单调性，奇偶性等）后，通过研究基本初等函数不仅加深了对函数的理解，而且掌握了幂函数，指数函数，对数函数，三角函数等非常有用的函数模型。类似地，在了解了数列的一般概念后，我们要研究一些具有特殊变化规律的数列，建立它们的通项公式和前n项和公式，并应用它们解决实际问题和数学问题，从中感受数学模型的现实意义与应用，下面，我们从一类取值规律比较简单的数列入手。新知探究1.北京天坛圜丘坛，的地面有十板布置，最中间是圆形的天心石，围绕天心石的是9圈扇环形的石板，从内到外各圈的示板数依次为9,18,27,36,45,54,63,72,81 ①2.S，M，L，XL，XXL，XXXL型号的女装上对应的尺码分别是38,40,42,44,46,48 ②3.测量某地垂直地面方向上海拔500米以下的大气温度，得到从距离地面20米起每升高100米处的大气温度（单位℃）依次为25,24,23,22,21 ③
人教版高中数学选择性必修二等差数列的概念（2）教学设计
二、典例解析例3.某公司购置了一台价值为220万元的设备，随着设备在使用过程中老化，其价值会逐年减少.经验表明，每经过一年其价值会减少d(d为正常数）万元.已知这台设备的使用年限为10年，超过10年 ，它的价值将低于购进价值的5%，设备将报废.请确定d的范围.分析：该设备使用n年后的价值构成数列{an}，由题意可知，an＝an－1－d (n≥2). 即：an－an－1＝－d.所以{an}为公差为－d的等差数列.10年之内（含10年），该设备的价值不小于（220×5%=）11万元；10年后，该设备的价值需小于11万元．利用{an}的通项公式列不等式求解．解：设使用n年后，这台设备的价值为an万元，则可得数列{an}．由已知条件，得an＝an－1－d（n≥2）．所以数列{an}是一个公差为－d的等差数列.因为a1＝220－d，所以an＝220－d＋(n－1)(－d)＝220－nd. 由题意，得a10≥11，a11＜11. 即：{█("220－10d≥11" @"220－11d＜11" )┤解得19<d≤20.9所以，d的求值范围为19<d≤20.9
人教版高中数学选择性必修二数列的概念（1）教学设计
情景导学古语云:“勤学如春起之苗,不见其增,日有所长”如果对“春起之苗”每日用精密仪器度量,则每日的高度值按日期排在一起,可组成一个数列. 那么什么叫数列呢?二、问题探究1. 王芳从一岁到17岁，每年生日那天测量身高，将这些身高数据（单位：厘米）依次排成一列数：75,87,96,103,110,116,120,128,138，145,153,158,160,162,163,165,168 ①记王芳第i岁的身高为 h_i ，那么h_1=75 , h_2=87, 〖"…" ，h〗_17=168.我们发现h_i中的i反映了身高按岁数从1到17的顺序排列时的确定位置，即h_1=75 是排在第1位的数，h_2=87是排在第2位的数〖"…" ，h〗_17 =168是排在第17位的数，它们之间不能交换位置，所以①具有确定顺序的一列数。2. 在两河流域发掘的一块泥板（编号K90，约生产于公元前7世纪）上，有一列依次表示一个月中从第1天到第15天，每天月亮可见部分的数：5,10,20,40,80,96,112,128,144,160,176,192,208,224,240. ②
人教版高中数学选择性必修二函数的单调性(1) 教学设计
1．判断正误(正确的打“√”，错误的打“×”)(1)函数f (x)在区间(a，b)上都有f ′(x)＜0，则函数f (x)在这个区间上单调递减． ( )(2)函数在某一点的导数越大，函数在该点处的切线越“陡峭”． ( )(3)函数在某个区间上变化越快，函数在这个区间上导数的绝对值越大．( )(4)判断函数单调性时，在区间内的个别点f ′(x)＝0，不影响函数在此区间的单调性．( )[解析] (1)√ 函数f (x)在区间(a，b)上都有f ′(x)＜0，所以函数f (x)在这个区间上单调递减，故正确．(2)× 切线的“陡峭”程度与|f ′(x)|的大小有关，故错误．(3)√ 函数在某个区间上变化的快慢，和函数导数的绝对值大小一致．(4)√ 若f ′(x)≥0(≤0)，则函数f (x)在区间内单调递增(减)，故f ′(x)＝0不影响函数单调性．[答案] (1)√ (2)× (3)√ (4)√例1. 利用导数判断下列函数的单调性:（1）f(x)=x^3+3x; （2） f(x)=sinx-x,x∈(0,π); (3)f(x)=(x-1)/x解: (1) 因为f(x)=x^3+3x, 所以f^' (x)=〖3x〗^2+3=3(x^2+1)>0所以f(x)=x^3+3x ，函数在R上单调递增，如图（1）所示
第四单元《教学设计》 说课稿 2021—2022学年统编版高中语文必修下册
（六）说教学策略1.专题性海量的媒介信息必须加以选择或者整合，以项目为依据，进行信息筛选，形成专题性阅读与交流；培养学生对文本信息“化零为整”的能力，提升跨媒介阅读与交流学习的充实感。2.情境化情境教学应指向学生的应用，建构富有符合时代气息的内容，与生活经验更加贴合，对学生的语言建构与运用有所提升，在情境中能够有效地进行交流。3.任务化以任务为导向的序列化学习，可以为学生构建学习路线图、学习框架等具体任务引导；或以跨媒介的认识与应用为任务的设置引导；甚至以阅读和交流作为序列化安排的实践引导。4.整合性跨媒介阅读与交流是结合线上线下的资源，形成新的“超媒介”，也能实现对信息进行“深加工”，多种媒介的信息整合只为一个核心教学内容服务。5.互文性语言文字是语文之生命，我们是立足于语言文字的探讨，音乐、图像、视频等文本与传统语言文字文本形成互文，触发学生对学习内容立体化和具体化的感悟，提升学生的审美能力。
人教版高中英语必修3Astronomy the science of the stars说课稿3篇
Step 2 Pre-listeningAfter students finish their discussion, I will show a picture of Newton and ask them: Who is him? What is he famous for? Could you find out some words to describe him? Maybe students will answer that he is genius for his finding of theGravitation, making a great contribution to the progress of human being. At that time I will show another two pictures of Einstein and Hawking, letting students guess who they are and write down their idea about the Gravitation. For I have arranged them to search more information about the gravity before this class, Students have beenfamiliar with the topic and will not be afraid about this abstract conception, which is helpful for their listening.Step 3 While-listeningIn this step, students will be required to listen the material for three times. The first and listening is extensive listening and the second and third listening is intensive listening. In the first time, They are required to listen a material including Part 1 and Part 2 and choose the best summary of the listening text. After they choose the right answer, They also need work in group to explain what is wrong with the others. Then I will make a conclusion that we should pay attention to the first paragraph and last paragraph and some keys to get the main idea. By doing this, their capacity of generalization will have a great improvement.Before the second listening, I will ask students to scan the blank on the power point quickly and ask them to note down some key words .Then ask them to listen to the Part 1again and fill the first column of the chart. Maybe some students just show the ideas of these three scientists an still can’t catch their development of gravity. Therefore, I will ask them to listen to Part 2 again and fill in the rest. After finish the listening, I will give them ten minutes to discuss with their partner. I will also guidethem to improve their answers when they discuss with others.
新人教版高中英语选修2Unit 3 Food and Culture-Reading and thinking教学设计
The discourse explores the link between food and culture from a foreign’s perspective and it records some authentic Chinese food and illustrates the cultural meaning, gerography features and historic tradition that the food reflects. It is aimed to lead students to understand and think about the connection between food and culture. While teaching, the teacher should instruct students to find out the writing order and the writer’s experieces and feelings towards Chinese food and culture.1.Guide the students to read the text, sort out the information and dig out the topic.2.Understand the cultural connotation, regional characteristics and historical tradition of Chinese cuisine3.Understand and explore the relationship between food and people's personality4.Guide the students to use the cohesive words in the text5.Lead students to accurately grasp the real meaning of the information and improve the overall understanding ability by understanding the implied meaning behind the text.1. Enable the Ss to understand the structure and the writing style of the passage well.2. Lead the Ss to understand and think further about the connection between food and geography and local character traits.Step1: Prediction before reading. Before you read, look at the title, and the picture. What do you think this article is about?keys:It is about various culture and cuisine about a place or some countries.
新人教版高中英语选修2Unit 3 Food and Culture-Discovering useful structures教学设计
The newspaper reported more than 100 people had been killed in the thunderstorm.报纸报道说有一百多人在暴风雨中丧生。(2)before、when、by the time、until、after、once等引导的时间状语从句的谓语是一般过去时，以及by、before后面接过去的时间时，主句动作发生在从句的动作或过去的时间之前且表示被动时，要用过去完成时的被动语态。By the time my brother was 10, he had been sent to Italy.我弟弟10岁前就已经被送到意大利了。Tons of rice had been produced by the end of last month. 到上月底已生产了好几吨大米。(3) It was the first/second/last ... time that ...句中that引导的定语从句中，主语与谓语构成被动关系时，要用过去完成时的被动语态。It was the first time that I had seen the night fact to face in one and a half years. 这是我一年半以来第一次亲眼目睹夜晚的景色。(4)在虚拟语气中，条件句表示与过去事实相反，且主语与谓语构成被动关系时，要用过去完成时的被动语态。If I had been instructed by him earlier, I would have finished the task.如果我早一点得到他的指示，我早就完成这项任务了。If I had hurried, I wouldn't have missed the train.如果我快点的话，我就不会误了火车。If you had been at the party, you would have met him. 如果你去了晚会，你就会见到他的。
新人教版高中英语必修1Unit 3 Sports and Fitness-Listening and Speaking & Listening and Talking教案
Finally, after finishing the task above, the teacher is expected to instruct students to work in groups to finish the following project:Speaking ProjectWhat event or activity would you like to invite your friend to? Make a conversation with a partner.Ski Race: Zhangjiakou, a beautiful city in northern China, will host the Youth Ski Race in December.Track Meet: a great event for track –and –field lovers on 26 October.Gym Class: come and work out at a gym! You can make it.Part 2: Listening and Talking:The teacher is advised to talk with their new students about the related topic: Boys and girls , what do you think of sportsmanship? Let’s listen and find out:Play the listening and match each opinion with the right speaker. Who do you agree with? Why?Cao Jing _____________ Lily _____________ Max _____________A. An athlete should do his/her best to win.B. The girl should stop and help the other girl. Good sportsmanship is more important than wining!C. An athlete should think about honor and his/her fans if he/she is competing for his/her country.Listen again and circle the expressions that you hear in the conversation.
新人教版高中英语选修2Unit 4 Journey Across a Vast Land教学设计
当孩子们由父母陪同时，他们才被允许进入这个运动场。3．过去分词(短语)作状语时的几种特殊情况(1)过去分词(短语)在句中作时间、条件、原因、让步状语时，相当于对应的时间、条件、原因及让步状语从句。Seen from the top of the mountain (＝When it is seen from the top of the mountain), the whole town looks more beautiful.从山顶上看，整个城市看起来更美了。Given ten more minutes (＝If we are given ten more minutes), we will finish the work perfectly.如果多给十分钟，我们会完美地完成这项工作。Greatly touched by his words (＝Because she was greatly touched by his words), she was full of tears.由于被他的话深深地感动，她满眼泪花。Warned of the storm (＝Though they were warned of the storm), the farmers were still working on the farm.尽管被警告了风暴的到来，但农民们仍在农场干活。(2)过去分词(短语)在句中作伴随、方式等状语时，可改为句子的并列谓语或改为并列分句。The teacher came into the room, followed by two students (＝and was followed by two students)．后面跟着两个学生，老师走进了房间。He spent the whole afternoon, accompanied by his mom(＝and was accompanied by his mom)．他由母亲陪着度过了一整个下午。
新人教版高中英语选修2Unit 1 Science and Scientists-Learning about Language教学设计
Step 7: complete the discourse according to the grammar rules.Cholera used to be one of the most 1.__________ (fear) diseases in the world. In the early 19th century, _2_________ an outbreak of cholera hit Europe, millions of people died. But neither its cause, 3__________ its cure was understood. A British doctor, John Snow, wanted to solve the problem and he knew that cholera would not be controlled _4_________ its cause was found. In general, there were two contradictory theories 5 __________ explained how cholera spread. The first suggested that bad air caused the disease. The second was that cholera was caused by an _6_________(infect) from germs in food or water. John Snow thought that the second theory was correct but he needed proof. So when another outbreak of cholera hit London in 1854, he began to investigate. Later, with all the evidence he _7_________ (gather), John Snow was able to announce that the pump water carried cholera germs. Therefore, he had the handle of the pump _8_________ (remove) so that it couldn't be used. Through his intervention，the disease was stopped in its tracks. What is more, John Snow found that some companies sold water from the River Thames that __9__________________ (pollute) by raw waste. The people who drank this water were much more likely _10_________ (get) cholera than those who drank pure or boiled water. Through John Snow's efforts, the _11_________ (threaten) of cholera around the world saw a substantial increase. Keys： 1.feared 2.when 3. nor 4.unless 5.that/which 6.infection 7.had gathered 8.removed 9.was polluted 10.to get 11. threat
新人教版高中英语选修2Unit 1 Science and Scientists-Discovering useful structures教学设计
The grammatical structure of this unit is predicative clause. Like object clause and subject clause, predicative clause is one of Nominal Clauses. The leading words of predicative clauses are that, what, how, what, where, as if, because, etc.The design of teaching activities aims to guide students to perceive the structural features of predicative clauses and think about their ideographic functions. Beyond that, students should be guided to use this grammar in the context apporpriately and flexibly.1. Enable the Ss to master the usage of the predicative clauses in this unit.2. Enable the Ss to use the predicative patterns flexibly.3. Train the Ss to apply some skills by doing the relevant exercises.1.Guide students to perceive the structural features of predicative clauses and think about their ideographic functions.2.Strengthen students' ability of using predicative clauses in context, but also cultivate their ability of text analysis and logical reasoning competence.Step1: Underline all the examples in the reading passage, where noun clauses are used as the predicative. Then state their meaning and functions.1) One theory was that bad air caused the disease.2) Another theory was that cholera was caused by an infection from germs in food or water.3) The truth was that the water from the Broad Street had been infected by waste.Sum up the rules of grammar:1. 以上黑体部分在句中作表语。2. 句1、2、3中的that在从句中不作成分，只起连接作用。 Step2: Review the basic components of predicative clauses1.Definition
新人教版高中英语选修2Unit 1 Science and Scientists-Reading and thinking教学设计
Step 5： After learning the text, discuss with your peers about the following questions:1.John Snow believed Idea 2 was right. How did he finally prove it?2. Do you think John Snow would have solved this problem without the map?3. Cholera is a 19th century disease. What disease do you think is similar to cholera today?SARS and Covid-19 because they are both deadly and fatally infectious, have an unknown cause and need serious public health care to solve them urgently.keys:1. John Snow finally proved his idea because he found an outbreak that was clearly related to cholera, collected information and was able to tie cases outside the area to the polluted water.2. No. The map helped John Snow organize his ideas. He was able to identify those households that had had many deaths and check their water-drinking habits. He identified those houses that had had no deaths and surveyed their drinking habits. The evidence clearly pointed to the polluted water being the cause.3. SARS and Covid-19 because they are both deadly and fatally infectious, have an unknown cause and need serious public health care to solve them urgently.Step 6: Consolidate what you have learned by filling in the blanks:John Snow was a well-known _1___ in London in the _2__ century. He wanted to find the _3_____ of cholera in order to help people ___4_____ it. In 1854 when a cholera __5__ London, he began to gather information. He ___6__ on a map ___7___ all the dead people had lived and he found that many people who had ___8____ (drink) the dirty water from the __9____ died. So he decided that the polluted water ___10____ cholera. He suggested that the ___11__ of all water supplies should be _12______ and new methods of dealing with ____13___ water be found. Finally, “King Cholera” was __14_____.Keys: 1. doctor 2. 19th 3.cause 4.infected with 5.hit 6.marked 7.where 8.drunk 9.pump 10.carried 11.source 12.examined 13.polluted 14.defeatedHomework: Retell the text after class and preview its language points
新人教版高中英语选修2Unit 1 Science and Scientists-Using langauge教学设计
This happens because the dish soap molecules have a strong negative charge, and the milk molecules have a strong positive charge. Like magnets, these molecules are attracted to each other, and so they appear to move around on the plate, taking the food coloring with them, making it look like the colors are quickly moving to escape from the soap.Listening text:? Judy: Oh, I'm so sorry that you were ill and couldn't come with us on our field trip. How are you feeling now? Better?? Bill: Much better, thanks. But how was it?? Judy: Wonderful! I especially liked an area of the museum called Light Games.it was really cool. They had a hall of mirrors where I could see myself reflected thousands of times!? Bill: A hall of mirrors can be a lot of fun. What else did they have?? Judy: Well, they had an experiment where we looked at a blue screen for a while, and then suddenly we could see tiny bright lights moving around on it. You'll never guess what those bright lights were!? Bill: Come on, tell me!? Judy: They were our own blood cells. For some reason, our eyes play tricks on us when we look at a blue screen, and we can see our own blood cells moving around like little lights! But there was another thing I liked better. I stood in front of a white light, and it cast different shadows of me in every color of the rainbow!? Bill: Oh, I wish I had been there. Tell me more!? Judy: Well, they had another area for sound. They had a giant piano keyboard that you could use your feet to play. But then, instead of playing the sounds of a piano, it played the voices of classical singers! Then they had a giant dish, and when you spoke into it, it reflected the sound back and made it louder. You could use it to speak in a whisper to someone 17 meters away.? Bill: It all sounds so cool. I wish I could have gone with you? Judy: I know, but we can go together this weekend. I'd love to go there again!? Bill: That sounds like a great idea!
新人教版高中英语选修2Unit 2 Bridging Cultures-Discovering useful structures教学设计
The grammar of this unit is designed to review noun clauses. Sentences that use nouns in a sentence are called noun clauses. Nominal clauses can act as subject, object, predicate, appositive and other components in compound sentences. According to the above-mentioned different grammatical functions, nominal clauses are divided into subject clause, object clause, predicate clause and appositive clause. In this unit, we will review the three kinds of nominal clauses. Appositive clauses are not required to be mastered in the optional compulsory stage, so they are not involved.1. Guide the students to judge the compound sentences and determine the composition of the clauses in the sentence.2. Instruct students to try to learn grammar by generalizing grammar rules, controlling written practice, and semi-open oral output.3. Inspire the students to systematize the function and usage of noun clause1.Instruct students to try to learn grammar by generalizing grammar rules, controlling written practice, and semi-open oral output.2.Inspire the students to systematize the function and usage of noun clauseStep1: The teacher ask studetns to find out more nominal clauses from the reading passage and udnerline the nominal clauses.
新人教版高中英语必修1Unit 1 Teenage Life-Listening and Speaking & Listening and Talking教案
Step 2 Listening and Talking1. The teacher is advised to talk with their new students about the related topic: Boys and girls, do you know some structures to talk about future activities? Talking about future activitiesWe’ll …I plan to …There’ll be …I hope to …We’re going to …2. After their small talk, the teacher can move on by playing the listening and solve the following task.Underline the expressions in the sentences below Cao Jing and Max use to talk about the future.We’ll learn useful skills.I plan to improve my spoken English.There’ll be students from different schools.I hope to make new friends.We’ll talk about teenage life.I’ll learn to make a fire.There’ll be students from different countries at the camp.There’ll be some experts there to show us how to live in the wild.We’re going to learn about wildlife.I’m going to give a speech.I think I’m going to enjoy the activities.I think we’ll have a lot of fun.3. Work in groups. Plan a youth camp.Teacher make the Ss think of ideas for the camp. And they can use the questions below to get started. And have the Ss present their ideas for a youth camp to the class.●What kind of camp is it?●Who will be there?●What will they do?●What will they learn?
新人教版高中英语必修1Unit 2 Travelling Around-Listening and Speaking & Listening and Talking教案
【教学目标与核心素养】1. Instruct students to get main facts by listening and motivate them to talk about the topics about how to prepare for the trip and make reservations by listening and ultimately can make travel arrangements and reservations. 2. Develop students’ sense of cooperative learning and individual thinking capability. 3. Develop students’ different listening skills to solve different listening comprehensive problems.4. Help students to understand how to use the structures “the present continuous tense (be doing) is used to express future plans.【教学重难点】1. Teach students how to focus on key words, not on single words or grammar.2. Prompt Ss to talk about the related topics, such as how to prepare for the trip and make a travel plan.【教学过程】Step 1: Listening and SpeakingLead inThe teacher is advised to talk with their students about the places that they want to travel most both at home and abroad: boys and girls, if you have a chance to travel around the world, where will you go? After their small talk, the teacher can move on by finishing the following listening task:Before travelling, what do we need to prepare for the trip?