Ladies and gentlemen, I returned to this year in a time machine. In the year 2500, we are able to travel through time to any year in the history of the earth. This year is your last chance your lifestyle to save the earth.

    Beginning in the middle of the 20th century, a few people were worried about polluting the earth's water and air, but most people did not change their way of life. Instead, they continued to pour(倒) dangerous chemical(化学物品) and other waste into lakes and seas, to drive more and more cars and trucks, and to cut down trees.

By the year 2200, the earth's water was completely polluted. People could no longer drink water, and they had to use other types of liquids(液体). Scientists said that in the future there might be too many people on the earth. But not enough was done.

So by the year 2300, there were so many people that food became scarce. There was no water to grow food and all of the fish in lakes and seas died because of pollution. Terrible wars broke out between the rich and the poor. Scientists were working very hard to find another planet in space where humans could live.

By the year 2400, the air was too polluted for humans to breathe. So we had to leave the earth. But only the rich were able to leave. Where did we go? Nowhere. And everywhere. You see scientists did not find another safe planet, so now we must travel around the universe in our space ships. We are still looking for a place to call our home.

    So it is up to you to change history. There is still hope. You must change your lifestyle now, before it is too late.

    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!

    Thousands of years ago, people didn't know that the Earth moved. They thought the sun really did move across the sky. The Greek god Helios was said to drive the sun across the sky with his chariot (战车). But now, the way people think has changed. Nowadays, it is the sun that drives a "chariot" around the sky.

    What do I mean by this? Well, quite simply, there is now a plane (or "chariot") that is powered by the sun. It has special parts on its wings. These parts absorb (吸收) power from the sun. They absorb so much power that the plane can still fly even at night. In Greek mythology (神话), Helios had to take a break at night. It seems we're finally even more powerful than the gods themselves.

    This plane is called Solar Impulse. It will fly across the US in May. This is very important for the future of the world.

    Why is solar energy (太阳能) important? Well, other kinds of energy are known to cause problems. If you live in China, you've probably noticed the pollution. This is caused by burning coal and gas to make energy. The heat and chemicals created by burning these things give us power. But if we use power from the sun, we don't have to burn anything and there will not be any pollution.

    Solar energy is not entirely ready yet. It needs to be improved. But the best thing about it is that, unlike coal and gas, it doesn't run out. The Solar Impulse plane could pretty much keep flying forever. Of course, the sun's light will eventually run out too one day, but not for another 5 billion years. That's a pretty long flight.

    Last year, a special kind of glove came out. It was invented to help blind people to learn Braille, which is a special system for the blind to read by touching. Shaking motors (震动马达) are put on each finger of the glove. They can make different sounds to tell a user which letter he is touching. Recently, two British college students have invented another special glove for the blind. It can make the user feel small and quick movements. An ultrasonic sensor (超声波传感器) with a battery is put on the back of the glove. When the user wearing the glove is close to an object(物体), ultrasonic waves (超声波) from the glove are sent out (发出). As soon as they hit the object in front, the waves will return to the glove. Then the waves cause the glove to shake. And the ultrasonic sensor makes different kinds of sounds. The sounds make the user know how far he is from the object.

    In the college invention competition, the two students got first prize and won 1,540 pounds. One of the designers said, "Now the ultrasonic sensor on the glove is quite large. We're going to use the money to develop a smaller and lighter ultrasonic sensor."

    There are lots of objects that we see in the sky. During the day we see the sun. After the sunset in the evening, we see mostly the stars. Not all the lights in the sky that we see are really stars.

    Of course, we see the moon. Some of the other lights in the sky are planets. Planets revolve (转动) around the sun like earth does.

    Once in a while someone will see what they call a shooting star.

    Shooting star looks like a star that is moving quickly across the sky. Some people believe that seeing a shooting star will bring them good luck. It's hard to find shooting star because they disappear fast.

    The correct name for a shooting star is meteor. Besides very large objects like stars, planets and moons, space has lots of little objects. These can be rocks in space left over from old planets.

    These objects can even be as small as dust. These objects are called meteorites(陨石).

    When a meteorite gets close to the earth, it gets pulled towards the earth by gravity. Earth is surrounded by atmosphere. Atmosphere is made up of air and clouds. A meteorite blows up in the earth's atmosphere. This makes the short bright moving light in the night sky. A meteorite thus turns into a meteor.

    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!