Anything, no matter how luxurious it is, will become a necessity when it is widely used. This is true of many of the present luxuries, including mobile phones, cars, computers and many other things. It is known to all that the purpose of the development of science is to make things easy for the mankind, not for only a small number of people. Therefore, the first thing to do after a new invention occurs is to spread it so as to benefit as many people as possible. In the course of the spread, the luxury becomes decreasingly luxurious until in the end it becomes a necessity. This is an objective law, nothing can be an exception.

　　With the quick development of science and technology, the process for many things to become a necessity from a luxury will be greatly shortened. Anything that can be imagined will be invented and in no time becomes a necessity accessible to ordinary people.

　　Modesty

　　Modesty is one of the many qualities that cross - century young people should possess. It makes you foresee your imperfections. It gives you the impetus to go forward. Most important of all, it makes you accessible and creates favorable conditions for you in interpersonal contacts.

　　However, many young people do not seem to realize the importance of modesty. Some of them just feel satisfied with a little success, without the slightest desire to make further progress. Others have too high an opinion of themselves, totally ignoring other people' s suggestions and advice. Consequently, their immodesty often drives them up against the wall. Worst of all, immodesty takes many young people away from their colleagues and friends. Therefore they find fewer people with whom they can confide.

　　For you to be modest, the first thing to do is to have a full understanding of your deficiencies. No matter who you are and no matter how talented you are, you are unlikely to be all - powerful. In fact, you will always, in spite of your talents, find things about which you feel helpless. Besides, you should also admit other people's strong points and try your best to learn from them. If you keep these two points in mind, you are on the right path to developing modesty.

　The Importance of Physical Exercise

　　Everyone hopes to live happily in the world. Physical exercise is indispensable to a happy life. There is a famous saying: "Life lies on exercise." Although you will not necessarily die without regular physical exercises, they' II certainly help you live longer and more healthily.

　　Exercise is good for us to build our bodies. It helps co - ordinate the different parts of our bodies when we have sports. For example, we must try our best to co - ordinate the movements of the arms and legs when we play basketball, or we won't be able to shoot the basket. Exercise also benefits our organs. It lets the heart beat faster than usual, and then helps enlarge the blood vessels to protect us from heart attacks.

　　Exercise can also contribute to the development of our ability to response agilely. For instance, when you play table- tennis, you must try to reflect as quickly as you can so that you may fight back at the right position at the fight moment.

　　Exercise can also contribute to improving our mood. When you do exercise, you move a lot, and you have to be more active. It helps you become more optimistic.

　　Exercise will fill your life with various contents and make it more colorful.

　　What's more, exercise will help you get rid of your inertia. If you keep doing exercise regularly, you will never be a lazy person. Therefore, exercise has great effect on one's character.

　　In a word, exercise is helpful, important and absolutely necessary.

　　Air-conditioners

　　In recent years, the air- conditioner has become one of the many indispensable electrical appliances for thousands upon thousands of families, especially those in the south, where the intense heat overwhelms the earth throughout the summer. The advantages of the air- conditioner are self - evident. Armed with the ability to refrigerate, the air- conditioner makes you feel refreshing and comfortable no matter how hot it is outside. Thus it guarantees the efficiency of your work and the quality of your rest. Without it there would be no knowing what would happen to you in the dog days. Moreover, it can also create a proper condition in summer for the operation of computers -- the best friends of yours in the information age. Too high a temperature would make computers work improperly, causing much inconvenience for your daily life and work.

　　With all the advantages the air- conditioner offers, its disadvantages are also obvious. To begin with, the installment of the air - conditioner always involves the hole making in the wall, which undoubtedly makes the wall less pleasing to the eye than if not. Besides, the air- conditioned environment may make you more and more dependent on the air - conditioner, thus physically weakening your ability to cope with hot weather. Most important, the air - conditioned environment provides poor ventilation, and sometimes may even give rise to a strange kind of smell, which makes you feel dizzy and sick. Consequently, you will be in no mood for enjoying the cool air produced by the air- conditioner.