The earth is about 4,600 million years old. Modern man has lived on the earth for only 35,000 years, but during that time, we have changed our planet in many ways. Many of the things that we have done are good, but more are not good for the earth.

    Water pollution

    A lot of people, birds and fish die each day because of water pollution. Factories have polluted the land and the water. As a result, many river and lakes are now dead.

    Air pollution

    In big cities, factories, as well as cars, trucks and buses are the biggest cause of air pollution. Many people in cities now have bad health problems. For example, Mexico city used to be a beautiful sunny capital, but today it is almost covered by thick brown clouds.

    Soil pollution

    In order to have a good harvest, most of the farmers use chemicals too much on their fields. That's bad for the soil. But this kind of pollution is difficult to stop.

    Hope for the future

    These problems are very serious for our future, so all of us should do something to improve our environment. If we can stop pollution, our planet will become more and more beautiful and our health will be better. Let's be greener people.

    Birdwatching is a fun hobby. Many people enjoy it every day. You can also enjoy it. Birdwatching does not have to take a lot of time or money. With materials(材料) around your house, you can build a good birdhouse. You can start birdwatching in 30 minutes in your very own yard. It's very easy!

    Materials you will need:

    Milk box        ●Glue        ●Scissors      ●Brown paint        ●Tools for painting

    To build a better birdhouse

    ⒈Clean and dry the milk box.

    ⒉Glue the top of the milk box shut.

    ⒊Cut holes into the milk box for the birds to get into the birdhouse. The size you use will determine which birds use the house. You can cut one hole per side, or two. A good place to cut is about four inches(英寸) from the bottom(底部).

    ⒋Paint your milk box brown. The color helps the birdhouse mix with the tree.

    ⒌Cut holes into the milk box in the bottom of the box to let out any dirty things. Add at least two small holes on the top of the box. The top holes are to let in clean air. Do this after painting, or the paint could fill in your holes!

    ⒍Put the box in a tree. You can see the birdhouse from a window of your house. Now you can watch your birds in any weather!

    Are you a big fan of E. T. (Extraterrestrial) or aliens? Then you should read Extraterrestrial Civilizations (《地球以外的文明世界》) by American writer Isaac Asimov (1920~1992). In his 1979 book, Asimov looked at whether there is life beyond the Earth. He also talked about how we might be able to communicate with aliens someday. Asimov even told us that there are possibly about 500, 000 civilizations (文明) in the galaxy(银河系). The book may be a little out of fashion since it came out in the 1970s. But you'll still enjoy the good reasoning (推理 ) and imagination of it. Asimov was a science fiction(科幻故事) master. His most famous works talk about the relationship between robots and humankind.

    When we can see well, we do not think about our eyes often. It is only when we can not see perfectly that we come to see how important our eyes are.

    People who are nearsighted can only see things that are very close to their eyes. Many people who do a lot of close work, such as writing and reading, become nearsighted. Then they have to wear glasses in order to see distant things clearly.

    People who are farsighted face just the opposite problem They can see things that are far away, but they have difficulty reading a book unless they hold it at arm's length. If they want to do much reading, they most get glasses too.

    Other people do not see clearly because their eyes are not exactly the right shape. This, too, can be corrected by glasses. Some people'8 eyes become cloudy because of cataracts. Long ago these people often became blind. Now, however, it is possible to operate on the cataracts and remove them.

    When night fails, colors become fainter to the eyes and finally disappear. After your eyes have grown used to the dark, you can see better if you use the side of your eyes rather than the centers. Sometimes, after dark, you see a small thing to one side of you, which seems to disappear if you turn your head in its direction. This is because when you turn your head, you are looking at the thing too directly. Men on guard duty sometimes think they see something moving to one side of them. When they turn to look straight at it, they can not see it any more, and they believe they were mistaken. However, this mistake happens because the center of the eye, which is very sensitive in daylight, is not as sensitive as the sides of the eye after dark.

    Every day there is less and less space on Earth for rubbish. Yet every day we make more and more rubbish. What can we do? We can recycle some of our rubbish. Recycling means that the rubbish will be made into something that can be used again.

    Recycling helps Earth. And it saves space in rubbish dumps. Half of everything that we put into landfills could be recycled instead. In fact, most things made of paper, metal, glass and plastic can be recycled.

    Paper can be broken into small pieces and made into new paper. Steel and aluminum cans(金属雄)can be melted down(熔化)and made into new cans. The same is true of glass bottles. This can be done over and over again. Recycling doesn't take as much energy as making these things the first time. So we can use less of Earth's fuel resources.

    Plastic can be melted down, too. Then it can be formed into park benches, playgrounds and so on. Some people call plastic the "wood" of the future. Things made of plastic will last about 400 years-even if they stay outside in the weather. No wood can do that!

    Can dolphins (海豚) talk? Maybe they cannot talk with words, but they can talk with sounds. They show their feelings with sounds. Dolphins travel in a group. We call a group of fish a "school". They do not study, but they travel together. Dolphins are mammals (哺乳动物), not fish, but they swim together like fish in a school. Dolphins talk to the other dolphins in the school. They give information to the others. They talk when they are happy, sad or afraid. They say "welcome" when a dolphin comes back to the school. They talk when they play.

    They make some sounds above water. They make many more sounds under water. People cannot hear these sounds because they are very, very high. Scientists make tapes of the sounds and study them. Sometimes people catch dolphins for a large aquarium (水族宫). People can watch dolphins in a show. Dolphins do not like to be away from their school in an aquarium. They are sad and lonely. There are many stories about dolphins. They help people. Sometimes they save somebody's life. Dolphins' meat is good, but people do not like to kill them. They say that dolphins bring good luck. Many people believe this.