healthy eating教案

2024小学英语二年级人教版下册《HealthyEating》教案教学目标：1. 学习食物的名称，并能用英语正确表达出来。

2. 了解健康饮食的重要性，并能简单描述健康饮食的好处。

3. 能够使用Are you...?和Yes, I am./No, I'm not.来询问和回答自己喜欢的食物。

教学准备：1.漂亮的图片或卡片，上面印有不同的食物。

2.相关的教学素材，如视频、互动游戏等。

3.多媒体设备，能够播放图片、视频和音频。

教学步骤：Step 1: Introduction (引入) - 10分钟1. 教师向学生展示一个盘子，并在盘子里放上一些图示食物的卡片。

2. 教师问学生是否知道这些食物，学生可以用汉语回答。

然后，教师告诉学生今天的主题是关于健康饮食。

3. 教师播放一个有关健康饮食的视频，并与学生一起观看和讨论。

Step 2: Vocabulary (词汇) - 20分钟1. 教师向学生展示食物的图片或卡片，然后逐个教学生这些食物的英文名称。

2. 教师可以通过图片让学生感受不同食物的味道、形状和颜色，并引导学生用简单的英语表达这些感受。

例如，"This is a red apple. It tastes sweet."（这是一个红苹果。

它尝起来很甜。

）3. 学生个人或小组练习：- 学生可以用已学的食物词汇来描述自己喜欢的食物，并与同学分享。

- 学生也可以根据图片选择自己喜欢的食物，并用英语回答教师的问题。

例如，"Are you like ...? Yes, I am./No, I'm not."（你喜欢...吗？是的，我喜欢。

/不，我不喜欢。

）Step 3: Healthy Eating (健康饮食) - 30分钟1. 教师向学生介绍关于健康饮食的基本概念，并为学生提供一些简单的例子和解释。

2. 教师与学生一起讨论健康饮食的好处，例如保持健康、拥有更多的能量和更好的注意力等。

《Healthy eating》Teaching planMaterial: 6A Unit 10 Healthy eatingLearning objectives:At the end of this period, students are expected to1. use adjectives to make comparisons2. develop the skills of working in pairs or groups3. be aware of the importance of a healthy dietTeaching focus:How to use the sentence patterns :…healthier than…, …less healthy than…, …as healthy as…, …as unhealthy as…Difficulty in teaching:1. Students may have difficulty using “…less healthy than… ” correctly and freely2. Some students may have difficulty speaking confidently when facing all the class. Procedure:Practise moreThis shirt is 100 yuan. That shirt is 180 yuan.This shirt is __ than that one.This shirt is _ ___ as that one.2. Linda is helpful to others. But Mary is more helpful to others. Linda is _______ _______ than Mary.Linda is ______ _______ _____ as Mary.She is always late for school. He is sometimes late for school.She is _____ often late for school than he.He is _____ often late for school than she.4. Mike looked stronger than Jack three years ago.Jack looked _______ _____ than Mike three years agoJack ______ look ______ ______ as Mike three years ago.A: What do you usually have for breakfast/ lunch /dinner ?B : I usually have __________for breakfast/lunch/dinner. What about you?A : I usually ______________.B : Do you often have steamed food or fried food?A: _______________B: Your diet is ______________ my diet.。

初中备课UnitHealthyEating教案初中备课Unit Healthy Eating教案一、教学目标本节课的教学目标是使学生了解健康饮食的重要性，并学习一些有关健康饮食的知识，培养学生选择健康食物的能力及习惯。

二、教学内容1. 词汇学习：健康食物的名称及相关词汇；2. 阅读理解：阅读关于健康饮食的文章，回答问题；3. 听力练习：听取关于健康饮食的对话，回答问题；4. 语言运用：用所学的词汇和句型进行口语练习。

三、教学过程1. 预习导入- 利用图片或课件展示健康食物的图片，引发学生对健康饮食的讨论。

- 引出本课的主题：健康饮食。

2. 新课呈现- 学生观看视频或图片，了解不同种类的健康食物。

- 教师介绍健康食物的名称及相关词汇。

3. 词汇学习- 教师以示范和让学生模仿的方式呈现词汇，例如：fruit salad, whole grains, lean protein等。

4. 阅读理解- 学生阅读一篇关于健康饮食的短文，并回答相关问题。

可以在小组内进行讨论，然后全班分享答案。

5. 听力练习- 呈现一段对话或短文，内容关于健康饮食，学生仔细听后回答问题。

6. 语言运用- 学生以小组形式进行角色扮演，模拟在餐厅点餐的场景，运用所学的词汇和句型进行对话练习。

7. 总结- 教师对本节课所学的内容进行总结，并强调健康饮食的重要性。

- 教师鼓励学生在日常生活中选择健康食物，养成良好的饮食习惯。

四、教学资源及评价方式- 教学资源：图片、视频、课件、阅读材料、听力材料。

- 评价方式：课堂讨论、小组活动、阅读和听力题目的回答。

五、教学延伸- 学生可以在家完成一份关于健康饮食的调查报告，并在下节课上进行分享。

六、教学反思本节课通过丰富多样的教学形式，使学生对健康饮食有了更深入的了解，并通过口语练习促进了语言的运用。

同时，鼓励学生在日常生活中选择健康食物，培养了他们的健康饮食习惯。

然而，教学中应该注重学生的参与度，鼓励他们积极发言和互动。

Unit 13 Healthy eating 教案unit 13 healthy eating 教案2teaching aims:1.review the words learned in the last two periods.2.learn and master modal verbs:had better,should,ought toteaching important points:1.how to guess the missing word according to the given sentence.2.let the students learn how to give advice or opinion about something,especially master how to use“should,ought to,had better and their negative forms”to give advice.teaching difficult points:how to correctly use“should,ought to,had better and their negative forms”to give advice.teaching methods:1.review method to consolidate the words learned in the last period.2.explanation method to make the students master how touse“should(not),ought(not)to,had better(not)”correctly.3.individual,pair work to make every student work in class.teaching aids:1.a projector2.the blackboardteaching procedures:step ⅰ. greetingsgreet the whole class as usual.step ⅱ. word studyt:in the last two periods,we have learned something about diets.as we all know,we'd better eat healthy food,eat less or junk food,and we should develop healthy eating habits.only in this way can we keepup with the high pace of modern life.of course,we have also learned some important words and phrases.now let's review them.open your books.let's look at word study in this unit.you are given five minutes to find the words that fit the following descriptions.read first,then fill in it according to the meaning of each sentence.is that clear?ss:yes.t:ok.first do it by yourself.then discuss them in pairs.after a while,i'll ask some students to read the words.(teacher goes among the students and the students begin to doit.after a while,teacher checks their answers.)suggested answers:1.nutrient2.diet3.vitamin4.mineral5.fat6.sugar7.protein 8.calorystep ⅲ. grammart:now i want you to translate several chinese sentences into english.look at the screen.(show the following on the screen.)1.外面很冷，你最好穿上你的大衣。

healthy-eating-教学设计教学文案unit 2 Healthy eating教学设计（一）教材分析这是一篇介绍“饮食习惯”的文章，包括传统饮食习惯的改变日常饮食选择,旨在让学生明白健康的饮食习惯的养成是拥有健康体魄的前提。

本篇文章生词量较大（共有546个单词，其中包括34个生词），标题较抽象，各段主题句分布不太明显（大部分分布在段落中间）。

且大部分学生对饮食与健康的关系（如人体每天必须摄入的六种基本营养成分的来源、健康饮食的重要性、什么是绿色食品等）了解较少。

因此，本文的学习难度较大。

（二）教学目标根据新颁布的普通高中《英语课程标准（实验稿）》关于阅读课主要教学目标的具体描述，结合本课教学内容，具体从语言知识、语言技能、情感态度和文化意识三个方面制定如下教学目标。

1. 语言知识目标：a)使学生了解protein, calcium等基本营养成分的来源和主要功能，健康的饮食习惯是健康的保证，以及素食主义等信息。

b)学习掌握有关营养成分与食物的词汇，如：protein、calcium 、carbo hydrate 、fibre、 mineral、 vitamin 、vegetarian & vegan、green food and clean food 、eco-food and organic food等，以及 keep up with ，The same goes for…以及as 和only 引导的倒装句的用法。

2. 语言技能目标：a)使学生学会克服生词障碍，通过略读，寻找文章的主题句，理清文章的总体框架与脉络；通过查读，捕捉文章的重要细节，理解作者的写作意图。

b) 使学生学会运用各种猜词技巧，猜测部分生词在具体的语言环境的含义。

c) 使学生能够运用所学知识，用英语为自己所熟悉的一个人设计一份“h ealthy diet”，并阐明设计的依据。

3.情感态度与文化意识目标：a）使学生学会审视自己、审视食物，提高养成健康饮食习惯的意识。

高一教案 unit 13 Healthy eatingUnit 13 Healthy eatingPeriod 1I. Teaching aims:1. Warming up to make the students love talking after a long time no see.2. Do some listening to improve the students listening ability.3. Making simple dialogues to train the students speaking ability.4. New words: junk, contain, vitamin, ripe, plenty of, a bit (of), etc..II. Important points:1. Train the Students’ listening ability.2. Master the new phrase and sentence pattern and make the students be free to talk about eating habit and health.III. Difficult points:1. Learn the usage of the sentences pattern: I think that ---because---.2. Improve the students’ listening and speaking ability.IV. Teaching methods1 . Listening-and–answering activity to help the students go through with the listening material.2. Use both individual work and group or pair work to make every student work and think in class.V. Teaching procedures:Step 1 PresentationBegin the class with my own eating experiences. Encourage the students to tell about theirs. Make them say as many names of the food as possible. Get them to tell their feeling aboutdifferent kinds of food. Ask:What do you think are good eating habits?W hat will happen if we don’t have good habbits?Conclusion: Every day we have food. Food makes us feel full and happy and it also helps to build our bodies. But have you ever thought what you eat is junk food or healthy food? Today we re going to learn something about food.Step 2 Warming up1. Have the students open their books at Page 1 and look at the eight pictures of different kinds of food. Tell the names of the food first. Then discuss in pairs:which of them are junk foods? Why?Or which of them are healthy foods? Why?2. Ask your classmates what they like to eat. The students may have a discussion in pairs and then make a list of the food and decide whether what they like to eat is junk food or not.3. According to the discussion, fill in the table with real information.Step 3 Listening1. Tell the students they are going to have some listening training. Let them know that something is wrong with Mike. Make them listen to the tape once and tell what is the problem with Mike and what he did next.2. Look at Ex. 1 on P2 and listen to what happened to Mike. The students are to answer the questions in it after a short discussion.3. Listen to what Mike did next, and then answer the question in Ex. 2. A short discussion is allowed in pairs.Step 4 SpeakingEveryone wants to be healthy and strong. But sometimes weare not feeling well. Ask:What will you do if you don’t feel well?Say: When we’re ill, we’d better go and see a doctor and the doctor will look over us and give us some advice. Now we’re going to practice some everyday English used by doctors and patients. Go through the useful expressions on P3.Have the students look at the example above. Ask two students act as Dr Yang and Sharon and read the dialogue aloud. Have the other students underline some useful expressions they can find.Go through the three situations with the students on P2. Ask them to choose one of them and make up a dialogue in pairs according to the example given and then act it out.Step 5 ConclusionToday we’ ve done some listen ing and speaking, and learn how to give advice and some everyday English used between doctors and patients.HomeworkPreview the reading passage in this unit.Period 2I. Teaching aims:1. 1. Learn and master the following words and expressions: make choices, pace, diet, nutrient, muscle, bean, keep up with, fibre, mineral, chemical balance, fit, be good for, function, and be harmful to, etc.2. Improve the students’ reading ability and study the language points connected with the text..II. Important points:1. Train the Students’ reading ability.2. Master the new phrases and wordsIII. Difficult points:How to make the students understand the reading text better.IV. Teaching method1 . Fast reading for the students get the general idea first.2. Discuss after reading to understand the text better.3. Careful reading to get the detailed information.V. Teaching procedures::Step 1 PresentationAsk the students what in their mind are healthy foods and what are junk foods. Help them to get a conclusion that we must develop healthy eating habits.Step 2 Pre-readingShow the students the pre-reading questions. Get them to discussion in groups. Ask individual students to give a report about their own answers to them. Ask:What do you think of your own eating habit? Is it healthy or not?Step 3 Fast ReadingSay: today we come to the Reading. It’ s about a healthy diet and tells the importance of keeping healthy eating habits. Read the text quickly and find the answers to the questions on the screen..1. What do traditional diets often have?A. too much waterB. too much proteinC. too much fat and too many caloriesD. nutrients we need2. What can help our body fight disease and give us energy?A. vitamins, fibre and minerals.B. pork and fishC. waterD. calcium3. What contains a lot of protein?A. vegetablesB. fruitsC. vitaminsD. fish, meat and beans4. Why do some people become vegetarians?A. Because they believe it is healthier not to eat meat or they think we should not kill animals for food..B. Because they think meat is not "eco-foods".C. Because they think meat will make them Fat.D. Because riley think meat will make them thin.5. From the passage we can conclude that it is probably better, ifA. we eat less meatB. we have more fruitC. we have "eco-foods"D. we buy good food and keep a balanced diet.参考答案：CADADStep 3 Careful reading1. Give enough time to let the students read the text carefully again, and tell the main idea of each paragraph.2. The students read the text paragraph by paragraph. The teacher ask as many questions as possible for the students to answer. Give the students some explanations to some difficult sentences or phrases. Pay attention to the new words and expressions.3. Play the tape for the students to listen and follow.4. Give the students some time to ask questions about the points they don’t understand.Step 4 Post-reading1. Do post-Reading 1- 32. Discuss the questions below, first in pair, then with the rest of the class.(1)Why do people go to fast food restaurant?(2)Why is it not good for you to eat too much sugar and fat?(3)Why are crash diets and supplements so popular?(4)What can we do to keep a balanced diet?Step 5 ConclusionHave two top students to make a conclusion about what we have learned in this class and what we can learn from this text. The teacher should speak highly of their answers. If possible, add some necessary information.HomeworkGo through the whole text and retell it.Get prepared for next class.Period 3I. Teaching aims:1. Review the text learnt in the last period including useful words and expression.2. Learn how to use had better, should and ought to while giving advice.3. New words and phrases: ought to, column, gram, sticky, etc..II. Important points:1. Master the usages of had better, should and ought to.2. Remember the words from the text.III. Difficult points:How to use had better, should and ought to correctly in different situations.IV. Teaching methods:1. Group or pair work to get the students do better in class.2. Use competition to make the students active in class.V. Teaching procedures:Step 1 PresentationIn this class we’re going to review the words we learnt andalso learn how to give advice using had better, should, and ought to. Write them on the blackboard.Step 2 Word studyMake the students open their books at page 5 and look at this part.First make the students work out the words in pairs. Give them some time to remember the answers.A competition: Get the students to close their books. The teacher reads out the descriptions and the students are to speak out the words as quickly as possible. See which group get the most correct answers.Step 3 GrammarThe teacher can tell the students when people use had better or had better not, should or should not, ought to or ought not to. Write down one or two examples for each phrase and try to make sure that the students understand all the usages by asking them to give their own examples.Then have the students fill in the blanks in Ex. 1 on P5 in a right way.Step 4 PracticeRead through the title with the students and let them get clear about what they are going to do with this exercise. They will try to write letters giving advice. Read the letters asking for advice quickly, then write down four pieces of advice for each of them using had better (not) , ought (not) to or should (not) .Step 5 WorkbookBooks open at P72. Do Exx. 1-3.HomeworkGo over the grammar by finishing the exercises on P73 in grammar part.Period 4I. Teaching aims:1. Do some reading about Snacks.2. Do some writing to develop the students writing skill..II. Important points:1. Train the Students’ writing ability by getting to know how to write a recipe..2. Improve their reading ability by reading this passage.III. Difficult point:Improve the students’ integrating skills.IV. Teaching methods1 .Asking-and –answering activity to go through the reading material.2. Individual and pair work.V. Teaching procedures:Step 1 RevisionCheck the answers to the exercises on P73 wit h the students Make sure all the students understand the grammar we learned in last class. If possible, go over it with the students.Step 2 Reading1. Skim the reading text and answer:What can we do if we need more energy besides eating our main meals?2. Read the text again quickly, do the following True-or-False exercises.1) Our body doesn’t need to refuel if we choose nutritious food for our main meals.2) Good snacks should come from different food groups and should not have too much fat or sugar.3) Fruits and vegetables don’t give us any vitamins.4) Most fruits need cooking.5) Fruits and vegetables are the only healthy snacks.参考答案：1. F2.T3.F4.F 5F3. Give the students some explanations when necessary.4. Play the tape and have the students follow. Give them some time to ask questions.Step 5 WritingGo through the two recipes on P7 carefully.Read the tips to the students to let them know for sure how to write a recipe.Have the students work in pairs and write the recipe for their favourite dish.Step 6 CheckpointUse Checkpoint 13 to help the students go over the grammar and useful expressions they have learned in this unit.HomeworkFinish off the workbook exercises.~。

HealthyEating教案
健康饮食教案
一、教学目标
1、让学生了解健康饮食的重要性，学会如何合理地搭配食物。

2、培养学生良好的饮食习惯，提高自我保健意识。

二、教学内容
1、介绍健康饮食的基本概念和意义。

2、讲解不同食物的营养成分和作用。

3、分析不良饮食习惯对身体健康的影响。

4、传授如何科学地选择食物和搭配的原则。

5、提醒学生注意饮食卫生，养成良好的饮食习惯。

三、教学步骤
1、导入环节通过展示一些常见的食物，让学生思考哪些食物对我们的身体健康有益，哪些食物对我们的身体健康有害。

2、知识讲解 a. 介绍健康饮食的基本概念和意义。

b. 讲解不同食物的营养成分和作用。

c. 分析不良饮食习惯对身体健康的影响。

3、实践环节通过课堂上的实物展示，让学生了解如何科学地选择食物和搭配的原则。

4、总结归纳通过总结，让学生回顾所学知识，明确健康饮食的重要性，并提醒学生注意饮食卫生，养成良好的饮食习惯。

四、教学反思
1、通过学生的反馈，评估学生对健康饮食的了解和掌握情况。

2、分析教学中存在的问题和不足，及时调整教学策略，提高教学效果。

3、提醒学生注意日常饮食中的问题，将健康饮食的理念融入到日常生活中。

五、作业布置
1、让学生回家后，根据所学知识，制定一份适合自己的健康饮食计划。

2、提醒学生在日常生活中注意观察食物的配料和营养成分，培养良好的饮食习惯。

Healthy eating 教案设计方案一、教材分析本节课通过讲述王鹏和永慧两家饭店的商业竞争，围绕健康饮食这个话题展开叙述。

通过谈论健康饮食，让学生了解饮食与健康方面的相关知识。

通过听力阅读丰富学生的饮食文化知识，教会他们如何改善饮食习惯，保持健康。

二、学生分析高一学生，具备了用英语沟通的基本水平。

但是，在阅读的速度、技巧方面还不足. 他们虽然对健康饮食有一定的了解，但是对他们来说流利的用英语表达自己的观点还是有一定困难的。

所以在阅读的设计上首先要激发学生学习的乐趣，层层铺垫。

其次阅读的设计要难度适中，让绝大部分学生都能够通过本堂课理解这篇文章并能够积极参与课堂。

三、教学目标使学生了解均衡饮食的重要性。

四、教学环节和效果在本堂课中，具体的使用环节和效果如下：1.在导入环节，利用图片引出本课主题，直观明了，有助于学生尽快进入话题氛围中，提升了课堂趣味性。

使用问题导入，能够从学生实际生活入手，使学生从一开始就感受到一种亲切感，能够很自然的导入文章主题。

2.在阅读环节，提前认真研读教材，将重要信息制作成PPT，使教学内容更加直观，课堂教学信息量增大，加快课堂教学节奏，同时补充了教学中的不足。

使用PPT能够很直观地表现文本阅读任务，引导学生一步步从skimming到detailed reading,学会阅读技巧，培养阅读水平。

由表及里，抓住本质，阅读问题的设计在内容上通过PPT，由浅入深，层次递进，由单一到发散，拓宽学生思维，在形式上，题型设计多样化，避免因题型单一而引起学生的厌倦心理。

五、教学设计Step 1. Lead-inWhat did you eat this morning? Do you want more choices?Step 2. Pre-reading1.PPT展示各种美食2．展示问题1)Tell what kind of food they are and how they can help us.2)Which kind of food do you like best? Which of them do you eat most often?3.听力听力任务1通过听一段对话连线每种疾病的原因1）Scurvy 2）Rickets 3）Obesitya.Too much rice, noodles, sugar and fat.b.Not enough vitaminc.Not enough protein and vitamin D听力任务2What is a balanced diet？A balanced diet needs __________like rice and______,_______________ like ______ and _______for protein and fat, and________________ like________ and _________for fibre and vitamins.4.Advertise your restaurant（通过这个话题导入课文）范例：Want to be fit and strong?Want to be slim and beautiful?Come and eat here.Our restaurant will give you a surpriseStep3. reading(阅读任务)1.Please read the text and fill in the chart2. Try to tell if these sentences are true or false.Step4. compositiondesign your balanced dietEverybody has to eat./Food plays an important role ……..From now on ,I will eat a balanced/healthy diet……I will eat…………… for breakfast/lunch/supper .Because it can help /make me……Keep fit/healthy /slim benefit /affect one’s health Step5. HomeworkPreview the language points and find out the difficult。

Unit 2 Healthy Eating教学设计Unit 2 Health Eating一、教法建议【抛砖引玉】单元双基学习目标Ⅰ四会单词和词组：pain , in (the) future , be rih in , ntain , fat ( n ) , sft drin , sre , sres f , disuss , disussin , at the end ( f )三会单词和词组：exaine , ripe , advise , patient , energ , eight , put n eight , esterner , ause , unhealth , lse eight , suggestinⅡ交际英语：人人都希望自己身体健康，工作顺利，生活愉快。

人体就像一部机器，机器需要经常保养才能不停地正常运转，不出故障；人也需要营养合理的饮食、充足的睡眠、必不可少的休息与娱乐。

倘若你为了省钱省时间而终日凑合着吃东西；倘若你为了挤出更多的时间对付艰苦的学习而挤掉了睡眠时间；倘若你为了多打工赚钱，几乎舍弃了所有的休息与娱乐。

那么，生病就在所难免。

万一人生了病就需要去医院诊断出出故障的原因，这时就需要和医生打交道，下面是常用到的语句。

医生用语：1 hat an I d fr u ? / hat as the atter ? / hat\’s the truble ?2 Des it hurt here ? / It\’s nthing serius / Let e exaine u / Tae this ediine three ties a da / And I advise u nt t d …3 Drin plent f ater and have a gd rest / u\’d better have a gd rest / u\’ll be ell sn4 Sh e ur tngue / Sti ut ur tngue / Did u ugh uh ? / Frtunatel , u nl have the flu (流感) / u\’ll have t be hspitalized (住院)H lng have u been lie this ? / ell , let\’s see pen ur uth and sa “ah ” / eep ar and dn\’t ath ld病人用语：1 I\’ve gt a pain ( ugh , headahe , tthahe ) / I dn\’t feel ell / There\’s sething rng ith … / This plae hurts / I feel a great pain here / I feel dizz (头晕) / I t se ediine last night , but the didn\’t help / Dtr , please give e an exainatin2 I\’ve had teperature taen I indeed have a fever / I as ht and ld b turns3 I dn\’t feel ell , dtr / I hpe it n\’t last lng / I dn\’t feel lie eating anthing4 I have a sre thrat ( 喉咙痛) and hest hurts / It started bthering e esterda afternn / I feel ht and feverish / I\’ ahing all verI\’ve been lsing sleep / hle bd feels ea / I\’ve lst vie / ears are ringing , and hees burning / I feel a pain in left legⅢ语法重点：进一步学习提出建议和忠告的句型。

人教版高中英语必修3《Unit2Healthyeating》教案人教版高中英语必修3《Unit 2 Healthy eating》教案【一】教学准备教学目标1. Get students to learn the useful new words and expressions in this part: cucumber, eggplant, pepper, mushroom, peach, lemon, nut, pea, spaghetti, diet, curiosity, customer, discount, ought to, lose weight, get away with, tell a lie, win…back.2. Let students have a better understanding of the reading passage.教学重难点mportant points1. Let students have a good understanding of the passage.2. Get students to learn different reading skills.◆ Difficult pointsGive students some guidance about how to choose the correct answers of the multiple choices according to some key words and key sentences.教学过程一学生课外学习活动设计：任务一：学生调查问卷：(1)What does a balanced diet should contain?(2) Why are you so strong/weak/fat/thin? Does it have anything todo with your diet?任务二：Making a diet for yourdinner.根据泛读学到的健康饮食的知识，为自己的家庭涉及晚餐食谱，分析食谱里包含哪些种类的食物，判断其能否提供均衡的营养，并分析原因。