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    Rivers are one of our most important natural resources(资源). Many of the world's great cities are located on rivers, and almost every country has at least one river through it that plays an important part in the lives of its people.

    Since the beginning of history, people have used rivers for transportation. The longest one in the United States is the Mississippi. The lifeline of Egypt is the Nile. To the people of India, the Ganges is great, but it is also important for transportation. Ships can travel along it for a thousand miles. Other great rivers are the Congo in Africa and the Mekong in southeastern Asia. The greatest of all for navigation(航海), however, is the Amazon in Brazil. It is so wide and so deep that large ships can go about two thousand miles up it.

    Besides transportation, rivers give food, water to drink, water for crops, and chances for fun and recreation for the people who live along their banks. In order to increase the supply of water for crops, engineers sometimes build a dam(坝) across a river and let a lake form behind the dam. Then people can use the water not only to irrigate(灌溉) their fields but also to make electricity for their homes and industries.

    However, large cities and industries that are located on rivers often cause problems. As the cities grow in size and industries increase, the water in the rivers becomes polluted with chemicals and other materials. People are learning the importance, however, of doing more to keep their rivers clean if they want to enjoy the benefits of them.

    Man has a big brain（大脑）. He can think, learn and speak. Scientist once thought that men are different from animals because they could think and learn. They know now that dogs, rats, birds can learn too. They are beginning to understand that men are different from animals because they can speak.

    Animals cannot speak. They make noises when they are afraid, or angry or happy. Apes（类人猿）can understand some things more quickly than men. One or two of them have learnt a few words. But they cannot put words together to make sentences. They cannot think as we do because they have no languages. The language is a wonderful thing. Man is able to build a modern world because he has language.

    Each child can speak his own language very well when he is four or five, but no animal learns to speak. How do children learn it? Scientists don't know. They only know that man can speak because he has the brain.

    The air pollution was so bad in Harbin, in China, on October 21, 2013 that the city had to close roads and schools, and cancel hundreds of flights from its airport.

    News reports said the smog (a mixture of smoke and fog) was so thick that people couldn't see more than 10 or 20 metres in front of them.

    It is also said that people could not even see the person standing next to them. The city's website said: "You can't see your own fingers in front of you."

    The local people said there was a "burning" smell in the air. Many people covered their noses and mouths with scarves or masks.

    The pollution was caused on several factors including: farmers burning off old corn stalks and crop stubble; coal-fired heating systems; and low winds that allowed the smoke to remain over the city.

    The smog had been building up for several days. It became worse when the city turned on the public heating system, which uses coal to heat millions of homes and offices in the city.

    Harbin has a population of more than 10 million people. It lies in northeastern China, where cold winter weather can last up to six months. The main fuel there is coal, because it is cheaper than other types of fuel.

    Air pollution from burning coal can cause health problems like heart disease. During the smog crisis* in Harbin, the number of people taken to the hospital with breathing problems was 30% higher than usual.

    The city government is trying to reduce its use of coal by adding more insulation and better roofs and windows to buildings to reduce heating needs. It has also used cleaner fuel for cars and factories.

    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.