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    Air pollution is one of the most common types of pollution in the world nowadays. It is quite serious in many places, especially in big cities. It can do great harm to our environment such as making the earth warmer, causing acid rain or destroying the ozone layer. As for human beings, air pollution causes all kinds of breathing problems.

    There are several reasons for air pollution. Firstly, many cities have a lot of factories and there we need to make food, clothing and other things. Every year these factories pour millions of tons of smog into air. Secondly, power factories can also give out harmful air. For example, in 1986 there was a bad accident at a nuclear power station in Russia. A cloud of radiation crossed the whole Europe. It is said that 125,000 people died in Russia as a result of illnesses caused by this accident. Thirdly, there are more cars in cities now. Once they are out in the streets, they will take in fresh air and give out dirty gas. Besides, smoking cigarettes also makes air pollution worse as will as damaging(损害) our health.  

    Artificial intelligence (AI) (人工智能）is the ability of a computer program or a machine to think and learn. It is also a field of study that tries to make computers "smart". John McCarthy, a scientist, came up with the name "artificial intelligence" in 1955. Many things such as learning and problem solving can be done by computers, though not in the same way as we do.

    An unusual goal of AI research is to create computer programs that can learn, solve problems, and think logically(逻辑地）. At present we use the term Al for successfully understanding human speech, recognizing(识别）human faces, operating self-driving cars and competing in some game systems like Chess and AlphGo（阿尔法狗）. Some people also consider AI a danger to humans if it develops too quickly. Professor Stephen Hawking (霍金), a well-known British scientist, was not for this kind of technology.

    Math is the basic language of AI. If we raise the standard in the learning of math, our students will be more likely to become successful AI designers in the future. We not only want bright students, but also need to attract average students and give them the math skills which are needed to change them into AI designers. Besides, a good knowledge of computer science is also necessary for AI designing.

    Scientists hope to create creative and emotional AI which can possibly understand human feelings or create art. Many ways and tools have been tried to discover this fascinating field.

    Trees are one of the oldest " citizens (公民) " of our Earth. They keep our air clean, reduce noise pollution, improve water quality and provide food and building materials.

    Just like us, trees change a lot as they grow. At 1 to 3 years old, young trees learn how to protect themselves. For example, many trees grow thorns( 刺) to warn animals not to go near. Most young trees have large, deep green leaves so that they can catch enough sunlight and change it into their food and energy.

    When trees are 4 years old, they begin to grow very rapidly and become strong enough to face challenges later in life. At the age of 15, trees become young adults. They grow more slowly and begin to produce flowers and fruit.

    It is not until the tree is 20 to 25 years old that it becomes a real adult. The tree reaches its largest size. The adult tree gives us shade, oxygen and natural beauty; it is also a great place for a tree house, or a place for us to read a book, listen to music and so on. If we give the adult tree proper care, it will go on to live healthily for many years.

    Gradually, trees begin to grow older and older and even die. At this time, they still have their important place in nature. When a tree becomes hollow (空心的) or part of it becomes dead, it provides a home to small animals and is a source of food for many other animals.

    In many ways, the life of a tree is similar to our own life experience. When we are looking at the life of a tree, we learn about that each period of life brings its own form of joy and challenge.

    Enjoy every minute of the life of the trees and take care of the trees!

    Carrots (胡萝卜) are grown on farms and in small family gardens all over the world. They are easy to plant and easy to harvest (收获). They have a good taste.

    When people think about carrots, a picture of a long, thin, orange-colored vegetable usually comes into their minds. But carrots come in many different sizes and shapes. And not all carrots are orange.

Carrots should be grown in sandy soil that does not hold water for a long time. The earth also should not be too hard. To prepare your carrot garden, dig up the earth and turn it over (翻土).

    Weather, soil, condition and time affect (影响) the taste of carrots. Warm days and cool nights are the best time to grow great delicious carrots.

    The best way to decide if a carrot is ready to be harvested is by its color. Usually, the brighter the color is, the better the taste is.

    Most people do not know that carrots can be grown during the winter months. If the winter is not cold enough to freeze the ground, you can grow and harvest carrots the same way as you do during the summer months.

Carrots are prepared and eaten in many different ways. They ate cut into thin pieces and cooked with other vegetables or meat. They are also washed and eaten just as they come out of the ground.

    Now satellites(卫星)are helping to forecast(预报)the weather. They are in space and they can reach any part of the world.The satellites take pictures of the atmosphere(大气), because this is where the weather forms(形成). They send these pictures to the weather station. So meteorologists(气象专家)can see the weather of any part of the world. From the pictures, the scientists can often say how the weather will change.

    Today, nearly five hundred weather stations in sixty countries receive satellite pictures. When they receive new pictures, the meteor- ologists compare(比较)them with earlier ones. Perhaps they may find that the clouds have changed during the last few hours .This may mean the weather on the ground may soon change, too. In their next weather forecast, the meteorologists can say this.

    So the weather satellites are a great help to the meteorologists. Before satellites were invented, the scientists could forecast the weather for about 24 or 48 hours. Now they can make good forecasts for 3 or 5 days. Soon, perhaps , they may be able to forecast the weather for a week or more ahead(提前)

    I like Saturday and Sunday because I don't have to go to school. 1do my mum and dad. On Saturday and Sunday I do not need to get up 2. Then I eat a light breakfast at about 8: 30. I always finish my homework on Saturday morning. In the afternoon, I do some housework. I also clean my own room and wash my own clothes. I think doing some houseworkis 3. In the evening, my family usually watch TV together and we talk a lot about the TV programmes. On Sunday, my parents and I go to see my grandparents. We go there by bike. It's a kind of good 4. Sometimes we go to the cinema or parties, 5we have a wonderful time at weekends.