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.

    Almost all animals need to sleep to stay healthy. But sleeping can also be dangerous because other animals may hurt those who are sleeping. This leads to many different ways of sleeping that help them stay safe. Some of these ways may surprise you!

    Almost all bats sleep upside down. They hang from a branch of a tree or the ceiling of a cave. Up high, bats are safe from most other animals. If they are in danger, they just fly away.

    A dolphin sleeps with just half its brain at a time. It must stay awake to breathe and to watch for danger. Dolphin mothers and babies can go without sleep for as long as two months to stay safe.

    Some ducks sleep with just half their brains, too. These ducks often sleep in a line. The ducks at both ends help to keep the group safe. They keep one eye open to watch for danger. The ducks in the middle sleep deeply with both eyes closed.

    Seals breathe air, but that doesn't stop some of them from sleeping underwater. They hold their breath and dive deep to sleep for up to twenty minutes at a time. Sleeping deep underwater helps these seals stay safe from animals that hunt them near the surface.

    Horses often sleep standing up. Their legs lock in place so they don't fall over. If a horse is lying down, it needs a long time to get up. A horse can run from danger more quickly if it is already standing.

    A flamingo can sleep while standing on one leg. The standing leg locks so it stays straight. The other leg remains close to the flamingo's body. Its head rests on its back. A flamingo lives (and sleeps) near many other birds to stay safe.

    Some seabirds can sleep while they fly. These large birds spend most of their lives over the ocean. They are in danger on the water, but they are safe in the air. They fly for many hours without flapping（拍打）their wings. Sometimes they sleep while they are flying.

    Would you like to sleep how they sleep?

    We know the mosquito very well. Mosquitoes fly everywhere. They can be found almost all over the world， and there are more than 2，500 kinds of them.

    No one likes the mosquito. But the mosquito may decide that she loves you. She？ Yes，she. It's true that male mosquito doesn't bite（咬） and only the female mosquito bites because she needs blood to lay eggs. She is always looking for things or people she wants to bite. If she likes what she finds， she bites. But if she doesn't like your blood，she will turn to someone else for more delicious blood. Next time a mosquito bites you，just remember you are chosen. You're different from the others！

    If the mosquito likes you，she lands on your body without letting you know. She bites you so quickly and quietly that you may not feel anything different. After she bites，you will have an itch（痒） on your body because she puts something from her mouth together with your blood. By the time the itching begins，and she has flown away.

    And then what happens？ Well，after her delicious dinner，the mosquito feels tired. She just wants to find a place to have a good rest. There，on a leaf or a wall， she begins to lay eggs，hundreds of eggs.

    Energy is everywhere. We use energy every day.

    Electricity is a form of energy and this is what powers the TV, hairdryer, phone, fridge, electric toothbrush and more! Our growing need for energy is one of the problems facing the world today, because producing electricity also produces pollution.

    Here are some simple ways to make a big difference when using electricity.

On or off? Leaving televisions and computers on with the little red light showing still uses electricity, even though they might look like they're turned off. To stop this you can turn them off.

    Lights out! Turning lights off when you're not in the room can save a lot of energy.

    Fridge door closed. The fridge is an important part of the kitchen, because it keeps food fresh, cool and healthy! But it takes a lot of energy to keep cool, so try not to leave the fridge door open or put hot things inside.

    Use the sun's energy. An increasing number of people are fitting solar panels（太阳能电池板） to their houses. They create electricity from sun-light, which can then be used to power our homes. Solar heating panels make hot water, reducing the need for electricity or gas.

    Every year on April 22, People all over the world celebrate Earth Day. It is a time to work to keep our earth clean. People plan projects to clean up the land, air and water.

    U.S. Senator Gaylord Nelson first thought of the idea for Earth Day in 1962 when he saw polluted rivers and cities with smoke. He needed to get support from Americans to clean up the earth. Finally, on April 22, 1970, 20 million Americans celebrated the first Earth Day! Now many countries around the world celebrate it, and you can, too.

    How can you celebrate Earth Day? Here are a few ideas:

    Join a clean-up project-Clean up your street or a favorite beach.

    Save energy-Turn off the lights when you leave a room, and use public transportation.

    Use less water.

    Reduce(减少)/ Reuse/ Recycle ― Practice the three Rs: First, reduce how much you use. Then reuse or recycle what you can.

    You can make a difference on Earth Day and every day!