Astronauts have already visited the moon and lived on space stations. They' ve never been to another planet, but they might visit Mars soon. The astronauts will spend about six months traveling to the planet, then about two years on the planet and about six months traveling back to the earth. They' ll be away from the earth for about three years, so they' 11 need a lot of food !

   It' s very expensive to take food into space. It costs about 120,000 dollars to carry something that weighs one kilogram. So an apple on Mars could cost 20,000 dollars! Of course, they will need to take quite a lot of food with them to feed the astronauts for three years. This amount of fresh food can not stay fresh, and is very expensive to take, so they need to find food that is not very heavy.     

   At the moment, astronauts on space stations eat dried food. It's very light, so it doesn't cost a lot of money to carry it into space. But astronauts stay healthier and happier if they eat fresh food. In the future, astronauts on Mars may grow vegetables like lettuce, spinach and carrots.

   Astronauts on Mars will probably have special machines. They' ll use these machines to change beans into foods that taste like meat or cheese because it won' t be possible to keep animals in space.

Millions of years ago, there were lots of trees on the earth, because summer lasted all year round. A forest covered the earth like a green carpet（地毯）．

What was that forest like? It is not difficult to find out, because parts of that ancient forest still stand. It is known as the rain forest. Here, even in fine weather water drips through the leaves.

The largest of today’s rain forests is inSouth America. It covers about a million square miles. All the trees are very tall. The young trees are up to 60 feet high. But it is not easy for some to grow taller, because very little sunlight reaches them.

The grown-up trees are about 60 to 120 feet high. Some are even taller. The tallest trees can be 200 or more feet high.

In this forest of tall trees, not only is plant life rich, but also is animal life. At different heights (高度) live different animals. By the many noises they make you know they are there.

All living things on the earth need other living things to live. Nothing lives alone. Most animals must live in a group, and even a plant grows close together with others of the same kind.  Sometimes one living thing kills another, one eats and the other is eaten. Each kind of life eats another kind of life in order to live, and together they form a food chain(事物链). Some food chains are simple, while others are not. But all food chains begin with the sun, and all food chains become broken up if one of the links（连环） disappears .

All life needs sunlight to live on. But only plants can use sunlight directly. Plants are "factories". They make food from sunlight, water and things in the soil and air.

Plants feed all other living things. Animals can only use the sun' s energy after it has been changed into food by plants. Some animals feed directly on plants, others eat smaller animals. Meat-eating animals are only eating plants indirectly.

What about human beings? We are members of many food chains. We eat wheat, rice, vegetables, and fruits and so on. We also eat meat and drink milk. But men often break up the food chains. They kill wild animals. They also make rivers, lakes and seas dirty. When these rivers， lake, sand seas are polluted, the fish in them can not be eaten. If men eat the fish, they will get strange diseases.

Each form of life is linked to all others. Breaking the links puts all life in danger

here are four inventions.

1  when it raina, do your shoes get wet ? Of course, they do! But you can buy these clever Umbrellas For Shoes. They keep the rain off your feet.

2  Do you have to clean the floor at home? Perhaps your cat can do a better job than you. Buy these Cleaner Cat Brushes. Then you can sit back and relax!

3   Do you talk too long on the phone? Most people do ! Save time---buy the Exercise Telephone! It weighs five kilograms. Then your calls will be less than five minutes long.

4   Do your friends sometimes come up behind you and make you jump? Do cars come around the corner when you try to cross the road ? Well, it won’t be a problem if you have Two-Way Glasses. You can look at things behind and in front of you at the same time.

Dolphins talk with sounds. They show their feelings with sounds.

Dolphins travel in a group. We call a group of fish a “school”. They don’t study, but they travel together. Dolphins are mammal（哺乳动物）, not fish, but they swim together in a school.

Dolphins talk to the other dolphins in the school. They give information（信息）. They tell when they are happy or sad or afraid. They say “welcome” when a dolphin comes back. They talk when they play.

They make a few sounds above(在···上面) water. They make many more sounds under water. People can’t hear these sounds because they are very, very high. Scientists make tapes of the sounds(录音) and study them.

Sometimes people catch a dolphin for a large zoo. People can watch the dolphin in a show. Dolphins don’t like to be away from their school in a zoo. They are sad and lonely.

There are many stories about dolphins. They help people. Sometimes they save somebody’s life. Dolphin meat is good, but people don’t like to kill them. They say that dolphins bring good luck. Many people believe this.

If music makes you smart and exercise helps you to think, surely exercising to music can turn you into a person who is better at learning and understanding.

A teamof scientists from Ohio State University did experiments on 33 volunteers. They found that person who exercised while listening to Italian musician Antonio Vivaldi’s The Four Seasons did much better in language ability (能力) tests than without music.

The volunteers said they felt better after exercising with or without the music. But their improvement on the test doubled (加倍) after listening to the music during exercise.” Exercise seems to causepositive changes in the nervous system (神经系统) and have a direct result on learning ability,” said the psychologist Charles Emery. Scientists have found that music can be good for health and education. It helps relieve stress, sadness and nervousness, encourages relaxation or sleep, wakes up the body and improves memory and thoughts.

Psychologists have been using Mozart’s music, especially his violin pieces, to help children with speech disorders (言语能力紊乱). Mozart is often chosen because his music is not over-exciting. A study shouted students who often exercise to Mozart’s music go on to score higher marks in tests. With important exams drawing near, your parents will not probably allow you to listen to music. But perhaps now you have good reasons to argue with them.

Energy is everywhere and we use it every day.

Electricity is a form of energy and this is what powers the TV, mobile phone, fridge 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(镶板) to their houses. They create electricity from sunlight, which can then be used to power our homes. Solar heating panels make water hot, reducing the need for electricity or gas.

What will the future be like? What do you think of it? Here are some answers from some students.

 Roy Burns: I think life in the future will be better. Most people in the world will use “green cars” by 2020, so there will be less pollution and people will live to be 200 years old. As for space travel, I would say, we will travel to Mars（火星）and some other stars in about fifty years.

Helen Lester: If we don’t take good care of the earth now, our children and grandchildren will be born into a world with too much pollution. There will be fewer trees and more buildings, because there will be more people.

Kitty Smith: I agree with Helen Lester. Things will be worse. The weather in the future will be much hotter. Human beings will have to look for another planet to live on.

Life in the future will be different from life today. Between then and now many changes will happen. But what will the changes be?

The population is growing fast. There will be many people in the world and most of them will live longer than people live now.

Computers will be much smaller and more useful，and there will be at least one in every home. And computer studies will be one of the important subjects in schools then. People will work fewer hours than they do now and they will have more free time for sports，watching TV and traveling. Traveling will be much cheaper and easier. And many more people will go to other countries for holidays.

There will be changes in our food，too. More land will be used for building new towns and houses for all the people. Then there will be less room for cows and sheep，so meat will be more expensive. Maybe no one will eat it every day. Instead，they will eat more fruits and vegetables. Maybe people will be healthier. Work in the future will be different, too. Robots will do dangerous and hard work. Because of this，many people will not have enough work to do. This will be a problem.

Do you like watching TV? Do you know the main difference between an HD-TV and a normal television? Let me tell you it’s the picture. It is clearer and more detailed (细腻).

   Every color television picture includes thousands of red, green and blue points. They all come together as an image (影像) in the eye of the person watching. The points are organized in lines that go across the television screen. There are more than five hundred lines in a normal television. The HD-TV has two times（倍数）as many as a normal television. To get this clear picture, you must have a big screen. Experts say people using a small screen will see little difference.

   The HD-TV also has clear sound. It is like the sound on a CD. All these improvements make an HD-TV very expensive. A major problem with the HD-TV is broadcast signal (传播信号).The signal is bigger than a normal television because it carries more electronic information.