Look at the centre circles of Diagram (图)A and Diagram B. Which of the centre circles looks larger? In fact, they are exactly the same size.
Then look at the picture on the right. What do you see? A vase? Or two faces？Does the picture change quickly from one to the other again and again? Maybe or maybe not, but you can never see them at the same time.

“What's happening? Is something wrong with my eyes?” You may wonder at what you see. Don't worry. Here is how it goes:
When we look at things, our eyes send messages to our brains and then our brains interpret（解读）the information. However, sometimes our brains interpret the received information in a wrong way. It seems that our eyes are playing a joke on us. This often happens and we call it “visual illusion(视觉错误)”.
Movie makers often make use of visual illusions. They make the objects around actors much smaller or bigger than usual. This makes us believe that the actors are much larger or smaller than they usually are. The movies Jurassic Parkand Honey I shrunk the kids just make use of visual illusions.

Radio, telephone and TV are widely used in the world. When you turn on the radio, you can listen. But when you use telephone, not only can you listen to others but also you can chat with them, however, you can't see anything at all. TV is much better than both of them. People can watch TV and listen to it, but they can't take part in what they see.

    Today, some people are using a type of telephone called vision-phone（可视电话）. With it, two people who are talking can see each other. It is better than radio, telephone or TV.

    Vision-phones can be of great use when you have something to show the person whom you are calling. It will be helpful in people's life. Some day you may be able to call up a library and ask to read a book on your vision-phone. You may be able to do some shopping too. Perhaps in the future, people will use vision-phone.

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    The koala is unique (独特的) to Australia and is an important symbol of the country. The koala is found in open eucalypt (桉树) forests in south-east Queensland. Even if it is called koala bear, this animal has nothing to do with the actual bear. Koalas have thick fur and large cars.

    Their broad, flat nose makes them look cute, similar to teddy bears. In fact koalas aren't cute. They have sharp teeth and very sharp claws (爪)! Koalas are marsupials (有袋类). This means the mother carries her baby in a pocket while it develops, similar to a kangaroo. The baby koala lives in its mother's pocket for the first six months of its life.

    The name “koala” comes from a native Australian word that means “no drink”. The koalas get almost all their water from the eucalyptus leaves they eat. That's where they get their food too.

    Koalas eat only eucalyptus leaves. The eucalyptus trees are where the koalas live, it's also where they sleep. Koalas sleep about nineteen hours a day!

    Why do they sleep so much? Some people think it's because they're lazy. But koalas aren't lazy. They sleep so much because there isn't much nutrition (营养) in eucalyptus leaves. Koalas store hardly any fat, so they must save their energy. One way to do this is to move slowly and sleep a lot. After a day of sleeping they like to move around and eat just after sunset. They live alone most of the time. Koalas are very protective of their trees. If a koala sees another koala eating in its favorite tree, it might tell the other koala to leave by “barking” at it. Koalas do “talk” to each other.

    Besides barks, the males make a deep grunting (呼噜的) sound.

    The mothers and babies talk in soft clicking sounds. If they get scared they may scream like a baby. The koala is also an excellent swimmer.

    They are able to cross rivers to escape from heavy flooding (泛滥).

    There are many wetlands in China and some of them have become the world's important wetlands. The Chinese Yellow Sea Wetlands are among them. They are in Yancheng, Jiangsu Province. They are home for many different kinds of birds and animals. The world's largest Milu Deer Nature Reserve(自然保护区) is in them. More than700 milu deer live freely there. There are not many red—crowned cranes in the world, but every winter you can see some in the Red—crowned Cranes Nature Reserve in the Yellow Sea Wetlands.

    The temperature in the wetlands is usually neither too high nor too low. There is a lot of rain and sunshine, too. They are usually good places for wildlife. Offering food and home for some special kinds of animals and birds is not the only reason why we need to protect wetlands. Wetlands are important because they also prevent(阻止) flood(洪水). But some people want to change the wetlands to make more space for farms and buildings. This means there will be less and less space for wildlife.

    Luckily, more and more people are beginning to realize(意识到) the importance of wetlands and wildlife. Every year, on February 2^nd, many activities are held to tell people more about wetlands.

    Zhalong is a nature reserve in Heilongjiang in northeast China．It is one of the world's most important wetlands．The area provides food and shelter for wildlife．It is an ideal home for different kinds of plants，fish and birds．

    Many birds live comfortably in Zhalong Nature Reserve all year round，while some only stay for a short time．There are many fish in the wetlands，and the birds can easily catch them for food．Zhalong Nature Reserve is an important living area for the rare red-crowned cranes．There are not manyred-crowned cranes in the world．Some of them live in Zhalong．

    Some people want to change the wetlands to make more space for farms and buildings．This means that there will be less and less space for wildlife．

    More and more birds are in danger because they do not have enough living space．Many of them died．The Chinese government wants to protect these endangered birds，and they can be safe in Zhalong．

    Every year a lot of tourists go to Zhalong to watch birds．This year members of ourBird watching Club are going to study the different kinds of birds in Zhalongand the changes in their numbers．The study begins next month．

    We do a bird count once a year．We are now inviting secondary school students to help．We need more people to help us count and do something to help the birds．Many people do not understand the importance of the wetlands．We hope this information will help them understand and make them actively take action to protect wildlife．

    The Internet joins millions of computers all over the world,and today it is used by people all over the world.It was invented in the 1960s in the USA.The American government needed a network of computers for its army.Then in the 1970s scientists and business people also wanted to use the Internet to send and receive messages.For some years,they weren't allowed to use the US network,and when they were allowed to,the messages were in very simple text without photos.

    The World Wide Web was invented by a British scientist named Tim Berners-Lee in 1989.He wanted to send documents to other scientists,so he developed the World Wide Web.This allowed him to send and receive scientific documents with text,drawings and photos(also called multimedia documents).In the 1990s,more and more people began to use the Internet and the World Wide Web.

    So what's the difference between the Internet and the World Wide Web?The Internet is the hardware.It allows us to communicate with other people.The World Wide Web is the software.It allows us to create, see and read multimedia documents.

    The Web is made up of millions of documents called Web pages.These pages are held in computers all over the world.Many people have a favorite website with a number of Web pages on the same subject.

    The email is a way of using your computer to send and receive messages.It's cheaper and quicker to use emails than send normal mails.New users call the normal mail “snail mail” because it's too slow.It took 50 years for 100 million people to listen to the radio.It took 15 years for 100 million people to watch television.By the year 2000, it had taken only about three years for 100 million people to use the Internet.What will happen next on the Internet?