my school 英语作文高中(通用20篇)

The Huang Mountain is a place of interest. here are lots of tourists seeing sights every day. Years ago, some of them paid no attention to environment protection. They threw about waste paper, plastic bags and tins. Besides, they killed animals, caught birds, destroyed trees and flowers. Worse still,

they often made a fire to cook in the forest. That was dangerous. Changes have taken place now. When tourists leave, they take away rubbish with them. They no longer hunt animals. Plants are also protected. All the tourists carry their lunch in order not to start forest fire. We must sing high praise of the good deeds.

Dear Mum and Dad,

Time flies! Ive been here for nearly a year. Im very pleased to find that our school is really a good one. The students in our school work hard at their lessons. They take an active part in activities that help to improve their qualities and health. They are friendly to each other and always ready to help each other.

The teachers here all enjoy their work and they love their students. They work hard and do what they can do to help their students. And the students respect their teachers. They get on well with each other. The students in our school try their best to kkp the school yard clean and tidy. They never throw waste about nor pick the flowers.

In a word, I am deeply impressed by the harmonious atmosphere in this school. I love my new school.

Yours,

Tom

亲爱的妈妈和爸爸，

时光飞逝！我来这儿已经快一年了。我很高兴发现我们学校真是一个好的学校。我们学校的学生在功课上努力工作。他们积极参加活动，帮助提高他们的素质和健康。他们彼此友好，随时准备互相帮助。

这里的老师们都喜欢他们的工作，他们喜欢他们的学生。他们努力工作，尽他们所能做的来帮助他们的学生。和学生尊重他们的老师。他们相处得很好。我们学校的学生尽力北校园干净整洁。他们从不乱扔垃圾，也不摘花。

一句话，我对这所学校的和谐氛围印象深刻。我爱我的新学校。

写作是对同学们英语综合能力的考查，是最能体现大家英语水平的一种检测方式。学生在写作的过程当中经常会暴露一些弱点、犯一些错误。今天，我们对大家英语作文中的常见错误进行简要归纳，并举以实例，大家在今后的英语写作中要尽量避免这些错误的发生。

一.名词

写作中，学生们常把握不好名词的数、所有格以及一些集合名词的用法。

1.Hegavemeaverygoodadviceyesterday.

句中的a要去掉，因为advice是不可数名词。一些汉语概念为可数的词在英语中却是不可数的，表示数量时在要其前加apieceof，类似的词有：news,bread,work,paper,chalk,furniture,information等等。

2.Thatgirllovesreadingbook.

可数名词单数不能孤零零地放在句子里，或前面加冠词，或将其变为复数。此处最好变为books.

3.Hewentintoabooksshopandboughtadictionary.

一般表示有生命的东西的名词的所有格用’s，如mymother’scar,而此处适宜用名词修饰名词，改为abookshop.

4.MyfamilyiswatchingTV.

一些集合名词如看成一个整体，则用单数的谓语动词，如Myfamilyisahappyone.如果强调集合中每个个体的个人行为，则用复数的谓语动词。此处看电视是个体行为，应把is改为are。类似的词有：team,class,audience等。

5.Iboughtsomepotatosandtomatosatthesupermarket.

中学阶段，以“o”结尾的名词中有四个词变复数时要加es，它们是tomato,potato,Negro,hero;其余的都加s变为复数。

6.Thishasnothingtodowiththeirbelieves.（这和他们的信仰没关系。）

以f,fe结尾的词变为复数时一般去f,fe加ves，如knife—knives,

thief—thieves;而roof和belief直接加s变为复数。所以应把believes改为beliefs.

二.冠词

7.Thebosswantstohireanusefulperson.

用a还是an，取决于后面单词音标中的第一个音，如为元音用an，为辅音用a。useful的第一个音是辅音所以应把an改为a。类似的，我们说aEuropeancountry.

8.Planeisamachinethatcanfly.

plane为可数名词单数，不能单独放在句中，应在其前加冠词或把它变为复数，而本句后有amachine,因此只能在其前面加a，变为Aplane。

9.Heplayedapianoatthepartyyesterday.

把a改为the，因为乐器前用定冠词。

10.Themachinewasinventedin1920s.

在in后加the，因为表示年代用in加the再加几十的复数，如在八十年代inthe80s。

11.XiaoHongwenttoschoolbythebuseveryday.

去掉the，因为表示交通方式用by直接加交通工具。

三.代词

使用代词时请注意其单、复数，主、宾格以及形容词性物主代词和名词性物主代词的用法。

12.Heisoneofthosespeakerswhomakehisideasperfectlyclear.

定语从句的先行词是thosespeakers，为复数，因此从句中的指示代词应为复数，应把his改为their。

13.Whomdoyouthinkhasleftthelightson?

放在疑问句特殊疑问词后的doyouthink/believe/guess/imagine/suppose等都不参与句子成分。本句中去掉doyouthink后缺的是主语，应把Whom改为Who。

14.ThebosspretendednottoseeJohnandI.

John和I在句中都做的宾语，应把I改为me。

15.Thesebooksaremine；thoseinthebagareher.

her是形容词性物主代词，后面应该加名词books，或把her改为hers。

四.数词

16.Therearefourteenhundredsstudentsinourschool.

hundred/thousand/million/score/dozen等词前有具体数字时后不加s，前面没有具体数字时在其后加s和of，表示大约几百几千的概念。如two

hundredstudents（两百个学生），hundredsofstudents（成百上千个学生）。例句中应把hundreds改为hundred。

17.Theirschoolistwiceaslargerasourschool.

表倍数关系的as...as中间只能用形容词或副词的原级。因此应把larger改为large.

18.Today’shomeworkisafive-hundred-wordscomposition.

几个单词由连字符连接而组成的复合形容词中的名词只能用单数，所以把five-hundred-words改为five-hundred-word.

19.TwothirdofthestudentsinourschoolarefromAmerica.

英语表达中分数的分子用基数词，分母用序数词，分子大于一时分母后要加s，所以就把third改为thirds.

五.形容词和副词

形容词和副词容易被误用，形容词和副词的比较级和最高级也是应注意的重点。

20.Thepatientappearednervouslywhenhetalkedtothedoctor.

appear在此是个系动词，其后应接形容词作表语。所以应把nervously改为nervous.

21.Theartistworkedhardlytofinishhisdrawingsontime.

此句需要一个副词来修饰，hardly是副词，但意为“几乎不”，hard也可以是副词，表努力，因此把hardly改为hard.

22.Thisshirtismorecheaperthanthatone.

more只构成比较级，而不能修饰比较级。因此把more去掉。

23.Heisthemostsuccessfulofthetwobusinessmen.

两者相比较时，比较级前用定冠词，三者或三者以上才用most，因此把most改为more.

24.Heworkslessharderthanheusedto.

表不如?...时用less加上形容词和副词的原级，因此把harder改为hard.

25.Thebookisfairlymoreinterestingthanthatone.

fairly只能修饰形容词和副词的原级，可以修饰比较级的副词或短语有：much,even,still,far,alot,alittle,abit,any,no,byfar,rather等，因此把fairly改为rather.

26.Thisisasaninterestingastoryastheoneinthemagazine.

as?as中间的词序是as加上形容词加上a(n)加上名词再加上as，因此应改为asinterestingastoryastheone.

27.Theweatherhereisnicerthan.

同样的事物才能相比较，weather和不具有可比性，因此应改为Theweatherhereisnicerthanthatof.

29.Iwouldrathertakeatrainthanwentbybus.

这个词组为wouldratherdo?thando?，因此把went改为go.

30.Isthereinterestinganythingatthemeeting?

修饰anything,something,everything,nothing的形容词都要放在它们的后面。

31.Ineverhaveseensuchapersonbefore.

像never之类的副词在句中应放在be动词、助动词之后，实意动词之前。因为应改为Ihaveneverseensuchapersonbefore.

32.Thebookisworthtoberead.

beworthdoing意为值得被做。因此改为Thebookisworthreading.

33.Itissurethathewillsucceed.

sure的主语只能为人，而certain的主语可为人和物。因此把sure改为certain.

34.Heisregardedasoneofthebestalivewritersatpresent.

alive为表语形容词，偶尔也做后置定语。因此把alive改为living，或把alive放在writers后面。

35.Idon’tknowthathehasfinishedtheworkyet.

yet用于否定和疑问句，already用于肯定句。把yet改为already.

36.Hesaidnearlynothingatthemeeting.

nearly不与否定词用在同一个句子中，而almost可以。因此把nearly改为almost。

六.介词

37.Heusuallygoestoschoolbyhisfather’scar.

by加上名词表示一种交通方式，中间什么都不加，如bycar,bybus,byplane等；如果名词前有其他的词修饰，则应用除by以外的其他介词，此处把by改为in.

38.Pleasewaitmeattheschoolgate.

wait为不及物动词，需加介词for后才能再跟名词或代词做宾语。

39.HehasbeenmarriedwithBettyformorethantwentyyears.

marry不跟with连用，应把with改为to。

40.Ifinishedtheworkontimeunderthehelpofhim.

Chinese New Year is the tradition festival in China.It is the same as the christmas day in the west country,it is welcome the new year.

It is the day that the families get together.

The spring festival is usually in the February ,sometimes in January.In the spring festival,every family all paste the lucky inscriptions,they fire the cracker,they eat the dumplings.The day before the new years first day is the new years eve,same as the christmas eve,all the families get together to have the new yaars dinner,wishes each other,talk about the wishes about the new year.Small children will receive the money given to children as a lunar new year gift.

Zeng Qiao is one of my friends. She is a beautiful, outgoing and good-tempered girl. She smiles frequently. I think it’s her smile that makes her beauty. We live in the same dormitory, so that we always stay together, no matter going to classroom or having dinners. At first, I don’t like her very much, because she is always talking. It seems that she can’t stop open her mouth. I am a little bit quiet and introverted, so I seldom talk to others. But gradually, I find that she can have influence on others by what she says. Zeng Qiao likes sharing interesting things with others. For example, she likes telling us her funny stories of her childhood or her former classmates. She always tells me that I should be more extroverted and learn to talk to others. Under the influence of her, I communicate with others more frequently and I find that it feels so great. I am so grateful that I can have such a good friend.

With the development of science and technology, smart phone becomes more and more popular. Even the students on campus begin to use handphone. Is it a good or bad thing?

随着科学和技术的发展，手机变得越来越流行，就连在校园里的学生也开始使用手机了。这到底是好还是坏？

Smart phone , on one hand, is good for students. For one thing , it enables students to keep in touch with their friends and family more conveniently and quickly. For another, it makes students fashionable and proud.

手机一方面来说对学生是有利的，举例来说，它能使学生与朋友和家人更方面快捷的取得联系。同时，它也使学生感到很时尚和骄傲。

On the other hand, smart phone has a negative effect on the students. First , it will cost them more money than before. Second, it will distract them from their study and life. Third, it will sometimes become a nuisance especially when it rings in classroom or in the library.

但另一方面，智能手机对学生也有负面作用。首先，手机会让学生们比以前花费更多的钱。其次，智能手机也让人更容易从学习和生活中分心。第三，智能手机让人感到麻烦和讨厌，尤其是在图书馆里或者是上课的时候。

so , smart phone is a good thing .However , the students should use it well .

所以，智能手机是个好东西，但是，学生们也要好好使用才行。

[高中英语作文：对手机的看法

I still remember the first time I went to the zoo.

When I was only five years old, my mother took me there.We took the camera and went to the station together. There were so many monkeys, tigers, lions, wolves and other animals in the zoo. We took many photos in the zoo with the animals. I was pleased to see so many real animals at the same time. They seemed so lovely and active.

I spent a nice day. But on my way home, I began to feel sorry for them. They were taken away from their parents and friends and also far away from the nature. They must have felt lonely, I thought. Every day, the only thing they could do was to sit there and wait for food.

我仍然记得第一次去动物园的那一天。

5岁那年，妈妈带我去动物园。我们带了相机一起过去。那里有猴子、老虎、狮子和狼等等，我们跟它们照了很多相。我很高兴能同时看见那么多活灵活现的动物，他们看上去又活泼又可爱。

我度过了快乐的一天。可是在我回家的路上，我开始替它们难过起来。人们把它们从父母和朋友身边捉走，它们一定感觉很孤单，我想。它们每天惟一可做的事就是等着人们来喂食。

The summer holiday is coming. Our class have had a discussion about what to do during the holiday. Some are in favor of staying at home. They think its both convenient and comfortable. Whats more, they can save money for other purposes. But they will lose the chance of getting to know the outside world.

However, others prefer to go out for traveling since it can increase their knowledge and broaden their horizons. But they will spend more money and meet some difficulties while traveling.

In my opinion, it would be much better to stay at home, for I can do what I like, such as reading books, watching TV, and helping my parents with the housework.

When I go to high school, our school has the rule to ask students to live

in the dormitory. Most students live with their parents before, so we all feel

excited and afraid of the group life. Luckily, I have three nice roommates. Soon

we become close friends. Living with others, we learn to do the house work, such

as everyone needs take turn to clean the floor, when we have something good to

eat, we will share with each other. The group life makes us have less private

space, but we enjoy the moment when we have the little talk before sleep, the

secrets that we dont want our parents know can talk to these girls. Whats

more, I become much independent. I learn to take care of myself and have really

grown up.

With the increasing use of cell phones, spam message has become a heated problem. According to a survey, on average, people receive about 40 pieces of spam message per month. Spam message can disturb, confuse, or even threaten people at any time.

Generally, there are two tesons for the spam epidemic. On one hand, due to the face that text message is a comparatively cheap channel, many companies take advantage of it to advertise their products or servies. Whether people are willing to receive the message is neglected. On the other hand, those holding lots of imformation on cell phone users sell the information and make money our of it.

To solve the problem of spam message, people should make joint efforts. The government should set up laws to severely punish the illegal advertisers and those who disclose information. Cell phone researchers and developers should upgrade the products and enable them to delete the spam automatically. Should people ace together, they will be free from the spam message.

As the Christmas Day is coming, our class decided to send some gifts to our

teachers, because we wanted to show our gratitude to them. At first, we had no

idea what to buy, because we wanted to do something special. So at last an idea

came to my mind. I advised to write a card, pasting some pictures of classmates

on it. Everybody agreed with me, so we spent a day to take some funny pictures,

and everybody wrote down their names on the card. When we sent this gift to the

teachers, they loved it so much. They were so impressed by this precious

surprise and would keep it forever.

27th, September of every year is World Tourism Day.

Of course, it is to advocate people to travel often.

Nowadays, as people’s living standard improve, the number and frequency of people to travel is also increasing. Why? I think it may because of the advantage of travel. First of all, travel can make people relaxed. In today’s competitive society, everyone is under great stress.

They may be crazy if they are in that situation in the long term. Going travel, leaving all the troubles behind for a period of time, people will have a good rest and then fight again. Secondly, travel can broaden people’s vision.

People can learn more through what they see and hear.

This knowledge is good for them. Last but not least, travel can enlarge people’s social circle, because they can make new friends on the way of their trip. In conclusion, travel has so many advantages. It is no wonder that there is a World Tourism Day to encourage everyone to go travel.

每年的月二十七是世界旅游日。当然，这是为了提倡人们多旅游而设的。

如今，随着人们生活水平的提高，去旅游的人数和频率都随之增加了。为什么会这样呢？我觉得可能是因为旅游所拥有的优势。首先，旅游可以使人放松。

在当今竞争激烈的社会，每个人都承受着巨大的压力。长期处于这种状态下，他们可能会疯了。

去旅行，把所有的烦恼暂抛脑后，人们将会得到良好的休息，然后再奋斗。

其次，旅游能开阔人们的视野。人们可以通过他们的所见所闻而学习。这些知识对他们是有用的。最后但并非最不重要的，旅行可以扩大人们的社交圈，因为他们可以在旅途中结识新朋友。总之，旅行有很多优点。难怪会有世界旅游日来鼓励大家去旅行。

[高中英语作文：旅游

Recently, the movies about the old people happen to have the magic and then

come back to their 20 years old time are very popular. The old people do all

kinds of crazy things that they never have the chance to do. These movies tell

people that given another chance, they will do whatever they want to do. I

always hear my parents said when they retired, they could carry out all kinds of

their plans and enjoyed the life. In my opinion, when we are young , we shuold

enjoy our moment and chase our dream. It is a little to carry out the plans when

we are old. Youth is the advantages.

It goes without saying that english plays an important role in our modern

society. english is an international language. wherever you go, you can hear

english spoken by many people.

From this point of view, it is true that english is important to our daily

life. learning english is like learning to swim or learning to play ball. our

primary trouble is that we have tackled the study of language from the wrong

end. we are like theman who thinks he can learn to swim only by reading books

about swimming. in actuality, we learn by doing. the grammatical rules are

valuable as we plunge into the language and need some assistance. in the same

way, advanced instructions about swimming are helpful as we learn something from

actual experience in the water. but reading books never makes a swimmer and

learning rules never makes a practical linguist. the regular procedure in

learning english involves listening first, to be followed by speaking. then

comes reading, and finally the writing of the language. the way you learn

english is much the same as the way you learned your own language.

First of all you must listen and then repeat and repeat until you can use

the language easily. in other words, you have to build up language habits in

english just as you build up english habits in your own language. to sum up, we

must bear in mind that nobody can learn to swim for you. nobody can learn to

play ball for you. nobody can learn english for you. its up to you. you must

learn for yourself and you will learn if you really want to and are willing to

practice.

A Day in the Zoo

There has been a long time for my family not to go out for the activity, because my father is busy all the time. But last week, my father finally finished his project, so that he could take a rest for some time. My father advised us to go to the zoo, I was so excited, because I hadn’t seen many animals in my life. In the zoo, there were so many people, it was so lively. I saw the monkey, the giraffe and so on. I saw these animals in the TV usually, but I saw them in front of me that day. The peacock impressed me so much, it looked homely when it laid down the ground, but when it stood up and opened the wings, it was so gorgeous. People said peacock was proud, indeed, it would not please people. I had a good time in the zoo.

对于我的家人来说，我们已经有很长一段时间没有外出活动了，因为爸爸总是很忙。但是上周，我的爸爸终于完成了他的项目，所以他能休息一段时间。爸爸建议我们去动物园，我很兴奋，因为我目前还没有看到过很多动物。在动物园里，有很多人，非常热闹。我看到了猴子，长颈鹿等等。我平常在电视上看到这些动物，但是那天我亲眼看到了。孔雀给我的印象很深刻，在它躺在地上的时候，看起来很普通，但是当它站起来，打开翅膀，是那么的美丽。人们说孔雀是傲慢的，确实，它不会取悦人们。在动物园里我度过了一段美好的时光。

[高中英语作文动物园一日游

Whatever we are, we should do our best!

When I was a little girl ,I dreamed to grow up. Because I think a child doesn‘t has freedom,and can‘t do anything himself.

But now I have grown up, to my surprise, I feel more tired and have more suffering.Though I can do something myself, I don‘t feel happy at all.

I believe you also have the same thoughs with me. when we was a child , we wanted to grow up, but when we became a older man,we don‘t have such nice life as wish. So whatever we are children or adults, we should try to make our life better, and make ourselves more happy. we should try our best to study hard, then we can let parents have good life, too! Let‘s do our best to do ourself ! Believe yourself ! You are the best!

[我们应该做最好高中英语日记

Oceans becoming more acidicThe worlds oceans are slowly getting more acidic, say scientists.The researchers from California say the change is taking place in response to higher levels of carbon dioxide in the atmosphere.The lowering of the waters pH value is not great at the moment but could pose a serious threat to current marine life if it continues, they warn.Ken Caldeira and Michael Wickett, from the Lawrence Livermore National Laboratory, report their concerns in the journal Nature.Increasing use of fossil fuels means more carbon dioxide is going into the air, and most of it will eventually be absorbed by seawater.

Once in the water, it reacts to form carbonic acid.Scientists believe that the oceans have already become slightly more acidic over the last century.But these researchers have tried to predict what will happen in the future by combining what we know about the history of the oceans with computer models of climate change."This level of acidity will get much more extreme in the future if we continue releasing CO2 into the atmosphere," said Dr Caldeira."And we predicted amounts of future acidity that exceed anything we saw over the last several hundred million years, apart from perhaps after rare catastrophic events such as asteroid impacts."If carbon dioxide release continues unabated, ocean pH could be reduced by as much as 0.77 units, the authors warn.It is not absolutely clear what that means for marine life, however.

Most organisms live near the surface, where the greatest pH change would be expected to occur, but deep-ocean lifeforms may be more sensitive to pH changes.Coral reefs and other organisms whose skeletons or shells contain calcium carbonate may be particularly affected, the team speculate. They could find it much more difficult to build these structures in water with a lower pH.In recent years some people have suggested deliberately storing carbon dioxide from power stations in the deep ocean as a way of curbing global warming.But Dr Caldeira said that such a strategy should now be re-considered."Previously, most experts had looked at ocean absorption of carbon dioxide as a good thing - because in releasing CO2 into the atmosphere we warm the planet; and when CO2 is absorbed by the ocean, it reduces the amount of greenhouse warming.

Yesterday my classmates and I went to on a picnic. According to our plan we would climb the West Mountain.

昨天我和我的同学去野餐。按计划要爬西山。

Early in the morning all of us gathered at the gate of our school, we started of at seven, soon it began to have a little rain. We kept on riding for an hour till we reached the foot of the mountain.

清晨，我们都聚集在学校门口，我们开始在七，很快就开始有一点雨。我们骑了一个小时，直到我们到达山脚下。

The little rain stopped then. We began to climb. Soon we reached the top of the mountain. How beautiful it was when we looked at the view from the top. We ran. sang, jump,

小雨停。我们开始爬山。我们很快就到达了山顶。它是那么美丽，当我们在山顶上看风景。我们跑了。唱歌，跳，

played chess, and had the pictures taken on the top of the mountain. and had lunch on the rocks. How happy we were!

下棋，还拍了照片在山顶。吃午餐的岩石上。我们是多么幸福!

After the lunch we went down the mountain. We got home at four, all of us almost gave out.

午饭后，我们下山了。我们四点到家，我们都筋疲力尽了。

ChenMo is my desk mate who is a good student in the eyes of classmates andteachers.

She is the first one to get to school every day.

Usually, she spendshalf an hour in learning English that takes us much to remember vocabularies andread the articles. Moreover, she not only focuses on her own study, but alsohelps other students in need.

Classmates like asking her for help, because sheis always ready for help.

However, I prefer to regard her as my friend ratherthan desk mate.

We communicate with each other frequently after class.

We discussour study as well as share our lives. She is desperately interested in playingbadminton, so do I. We would play badminton very Friday after class, whichhelps us relax ourselves as well build our body. It’s so great to have a deskmate that has interest in common.

陈茉是我的同桌，她是老师和同学眼里的好学生。她每天都是第一个到教室的。

通常，她会花半个小时学习英语。英语需要花比较多的时间去记单词和读课文。陈茉不仅专注于自己的学习，也积极帮助其他有需要的同学。

同学们喜欢找她帮忙，因为她总是那么乐于助人。

但是，在我眼里，她不仅是我的同桌，更是我的朋友。课后，我们经常相互交流，讨论学习问题或是分享彼此的生活。她很喜欢打羽毛球，我也一样。我们常常会在周五下课后打羽毛球，这不仅能使我们得到放松，也有益于我们的身体健康。能有一个拥有相同兴趣爱好的同桌真是太好了。

[高中英语作文：我的同桌

Since I go to middle school, I have to learn many subjects. Though I am not

the best student in class, but I won’t give up. I always tell myself to work

hard, because if I want to compete with other students, I need to make great

effort. People are easy to deny themselves when they face difficulty. If they

fail one time, then they will doubt the effort they have made. Actually, we are

not studying in vain. What we learn will be a great help to improve ourselves.

The thing we learn decides what kinds of person we are. So don’t deny yourself,

as you will see the value you have stored before in the future.

Currently,self-confidence has become the order of our life, which improves the theorythat nothing is more valuable than self-confidence.

如今，自信已经融入了我们的生活中了，这也就证明了没有什么能够比自信更有价值。

Itis obvious that self-confidence means trust in one’s ability. If we are full ofself-confidence, we’ll have creative power to live and work, helping us successor dreams come true. On the contrary, if we have no confidence in ourselves,there will be little possibilities for us to win. We’ll always face failure.

很明显，自信意味着对一个人能力的信任。如果我们充满自信，我们在生活和工作中就会有创造力，帮助我们成功或者实现我们的梦想。相反，如果我们对自己没有信心，我们取胜的可能性就很小。我们总是要面对失败。

What’smore, no one can deny another fact that self-confidence gives us light when wewalk in the dark and courage when we face stumbling blocks. Withself-confidence, we can achieve goals in our life.

再者，没有人能否认这样一个事实，当我们游走在黑暗时，自信能能给予我们光明，当我们遭遇不顺时，自信能给予我们勇气。有了自信我们可以实现生活中的目标。

[高中英语作文：自信的重要性