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We've all heard of mermaids. They are the beautiful half-human, half-fish creatures(生物). They have the head and body of a human and the tail of a fish. We also know that mermaids only exist in fairy tales. But where did all the stories about these creatures come from? If you have ever seen a manatee, then you might have an idea.
Manatees, which are also called sea cows, are mammals(哺乳动物) that live in the sea. Since they are mammals, they have to swim up to the surface to breathe air. Many people believe that the story of the mermaid began with the ancient sailors who saw the manatees putting their heads out of the water to breathe. Because manatees are upright when they do this, it looks like they are standing. If a sailor saw a manatee doing this from far away across the sea, it is possible that the sailor would mistake the manatee for a creature that is half-human, half-fish.
Mermaids are described as having very long hair. This is probably because manatees like to swim up to the surface of the water in areas where there is sea grass. Manatees eat all kinds of plants in the sea, including sea grass. The sea grass around the manatee's head when they eat could create a picture of long hair.

Manatees also have powerful tails that are very similar to the fish-like tail of a mermaid. The sailors probably watched manatees come up for air and then swim back below the surface, using their paddle-shaped tails. This would explain why the sailors thought mermaids had fish-like tails.

    There are many kinds of 1. transportation now. Which one do you like best, by train, by bus or by plane? Now let's look at these three kinds of transportation. 2.The fastest way to travel is by plane. If you want to save time, 3.乘火车是最好的选择. A plane ticket can also be easier to book, and there are 4.(hundred) of planes leaving half an hour to everywhere. But it is much 5.(expensive) than traveling by train or by car. Many people prefer to traveling together by train. Because the train is cheaper than the plane and you can see the beautiful scenery out of the windows. But sometimes people are very noisy on the train. And it's very small and crowded inside the train. Taking a car is great. You can feel freer in your own car and you can move quickly from place to place at any time you like. 6.But sometimes you may be late because of the heavy traffic  .You have to pay for a car park and petrol . Cars are less comfortable than trains. You can't sleep or relax when you drive. Cars pollute the air more than trains, too.

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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.

    Sitting too much is now listed with smoking and junk food as a bad habit that increases your risk of heart disease.

    New Australian research shows that half-an-hour in the gym will not make up for the waist-expanding damage caused by spending the rest of the day sitting.

    But the good news is that doing chores(家务杂事) in the house or gently walking around the office while on the phone might be enough to keep you fit.

    The study joins the growing body of evidence suggesting too much sitting might undo the benefits of exercise.

    The study measured the intensity(强度)of physical activities in 168 subjects over seven days. If found that, regardless of how much exercise they did or their total sitting time, those who took more breaks from sitting had lower risk of thick waists and lower levels of blood lipids(脂质).

    “Higher levels of blood lipids have been linked to a heightened risk of heart disease,”principal researcher Genevieve Healy of the University of Queensland said. "What the study shows is that there are benefits in just getting up regularly and interrupting your sitting time."

    Researchers behind the Stand up Australia project have written to the Rudd Government requesting $ 3.5 million for a two year study into how long sitting affects the health and productivity of workers.

    The latest study builds on work that is shifting the health promotion focus from purposeful exercise, such as running, to lower intensity activities throughout the day.

    The Australian research bas been backed up US studies, which show standing up is enough to double the metabolic(新陈代谢) rate and the amount of calories burnt.

    “To hold a body that weighs 77kilograms upright take a .fair amount of energy from muscles", said professor Marc Hamilton from the University of Missouri. "There is a large amount of energy associated with standing every day that cannot be easily replaced by, 30 to 60minutes in the gym."

    There have been many great inventions that changed the way we live. The first great invention was one that is still very important today—the wheel. This made it easier to carry heavy things.

    Then in the early 1800's the world started to change. There was little unknown land left in the world. People didn't have to explore(探测) much anymore. They began to work to make life better.

    In the second half of the 19th century, many great inventions were made. Among them were the camera, the light and the radio. These all became a big part of our life today.

    The first part of the 20th century saw more great inventions: the helicopter in1907, movies with sound in 1923, the computer in 1927, and jet planes in 1930. This was also a time when a new material was first made. Nylon(尼龙)came in 1937. It changed the kind of clothes people wear. 

    By this time most people had a very good life, and man has a desire to explore again. The world was known to man but the stars were not. Man began looking for ways to go into space. Russia made the first step. Then the United States took a step. Since then other countries, including China and Japan, have made their steps into space.

    New inventions will someday allow us to do things we have never yet dreamed of.