【正文】 f others, which were all luxuries years ago. Anything, no matter how luxurious it is, will bee a necessity when it is widely used. This is true of many of the present luxuries, including mobile phones, cars, puters 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 bees decreasingly luxurious until in the end it bees 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 bee a necessity from a luxury will be greatly shortened. Anything that can be imagined will be invented and in no time bees a necessity accessible to ordinary people.SupermarketsSince the first supermarket emerged fifty years ago, it has bee the most popular shopping center in many large cities around the world. In China, supermarkets enjoy an increasing popularity among city dwellers, especially the mon people with low ines. Compared with other types of stores, supermarkets are getting popular for several reasons. First, fewer employees are required in supermarkets and management cost is reduced. Second, almost all goods are shipped directly from the producers and sold at considerably cheaper prices. Lastly, in supermarkets, almost every kind of daily necessity is available and placed on open shelves, so the customers can choose whatever they want from their shopping list and take the items to the checkout counter easily. As a result, instead of visiting many stores, customers can get the tiring shopping task done quickly and feel relaxed. What is more, many supermarkets stay open very late at night, and provide large parking spaces. In the last few years, supermarkets have mushroomed in Beijing and many other large cities in China. The fort, economy and convenience of shopping in supermarkets please Chinese customers very much。 and the supermarkets, steadily gaining popularity, are doing booming business in China. Ine Sources of College Students　　According to the investigation of the ine sources of students, the ine of American and Chinese students es from parents, parttime job and scholarship, However, the percentage of each ine is quite different, Fifty percent of the American students ine es from their parents, fifteen percent es from the scholarships granted by colleges and universities and the rest es from parttime jobs. Ninety percent of Chinese students39。 ine es from their parents. 　　In my opinion, the main reasons for the difference is that American students are taught to be independent when they are very young, while Chinese students are taken such good care of that it is very difficult for them to live on their own. What39。s more, Chinese students have fewer opportunities to find parttime jobs. 　　Nowadays more and more Chinese students are seeking parttime jobs. For one thing, some students e from poor areas and their parents can39。t afford the high cost of education. For another, they39。re eager to acquire some social skills and earn some money which will help them do more in school and live independently, AS far as American students are concerned, I think the sources of American students39。 ine will remain the same. How to Keep Fit A healthy body is very important to every one of us. When you are sick, you feel painful all over your body, have no energy to work。 and the only thing you want to do is lying on the bed. When you are healthy, you can eat well, sleep well, sing and jump happily, do all the things you like to enjoy life. The methods to keep us fit vary. In the morning, you can get up early, go outdoors, breathe the fresh air, and do physical exercises. Running and swimming are extremely helpful to keep one fit. If you are a busy person and have no special time allocated to do these things, there are still some ways useful for to keep fit. The easiest way is to walk to your office instead of riding a bike or taking a bus. You also have to take a routine physical check up. Your doctor will know the condition of your body most clearly, and he will give you the most valuable advice to keep fit. You should always try to make yourself happy. If you feel happy, you can eat well, sleep well, and your body is sure to be in an excellent condition. Health is the most valuable possession a person expects in his life. Try every means to keep fit is my advice to the people who want to live a happy life in this beautiful world. Competition and cooperationCompetition is a mon phenomenon in our society . We pete when we play games, we try to do better than others in our study, and there is constant petition for jobs, fame, wealth and so forth. Therefore, we can say that, in a certain sense, petition is one of the motive forces of the development of our modern society. It is often believed, that petition and cooperation are in opposition to each other. Some people stress petition, without which, in their eyes, there is no responsibility, no drive and ultimately, no progress. Others advocate cooperation whatever they do. They are of the opinion that the dependence of people on one another has increased, without which the society we live in can not keep going smoothly. In reality, we find that in many cases petition goes hand in hand with cooperation. Let’s take a football game for example. During the game, one team is peting against the other, but each member of the team must cooperate with his teammates. Otherwise, they would lose the game no matter how skillful each individual player might be. It is clear that petition has much to do with cooperation. As far as I39。m concerned, I do not agree with the view that petition and cooperation are always i