Why don't birds get lost on their long flights (飞行) from one place to another? Scientists have studied this puzzle for a long time. Now they're starting to fill in the blanks(空白).

    Not long ago, experiments showed that birds use the sun to guide them during daylight hours. How do birds fly at night? Tests with artificial stars, which are made by people, have proved that certain night-flying birds are able to follow the stars in their long-distance flights.

    They found a bird that spent its lifetime in a cage and never flew under a natural sky. But it was born with the ability to use the stars to look for the direction. This bird's cage was placed under the sky filled with artificial stars. Any change in the position of the artificial stars caused a change in the direction of the bird's flight. From the experiment, they found that the bird tried to fly in the same direction as those artificial stars moving under the natural sky.

    But the stars are of course birds' main ways of navigation (航行), when the stars are hidden by clouds, they can still find their way by such landmarks (路标) as river courses, mountain ranges (山脉), coast lines and so on. Because of this ability, people use the dove (鸽子) to send messages in some fields. For example, the doves were used to send messages in both World War I and World War II. During that time, thousands of doves were used to carry important messages in order to save the lives of many thousands of people. So it is also the symbol of peace.

    But when it's too dark to see these things, the doves are not able to find their way. They only circle helplessly and get lost.

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    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 best time to collect green leaves is early in the leafing season but not so early．The months of June and July provide the best leaf samples（样品），but you can find great leaf samples throughout the summer．To make a fall color collection，you have to collect the leaves in autumn．

    I have seen many beautiful fall color collections．

    When you choose leaves for your samples，try to choose leaves of about the same size and shape on the tree．Make sure you collect the entire（完整的） leaves．

    Remember，some leaves have only one blade（叶片） or leaflet（小叶）．Some leaves have a few or many leaflets．You must know these two kinds of leaves．Good leaf collections contain the entire leaves．

    You should dry the collected leaves carefully before putting them in a leaf press（压）．When you collect leaves in the field，you can put them between the pages of book to protect them．And then，press them as soon as possible before you take them from this book．Finally，you should write down each leaf's name and put them in a leaf press．

    In 1969, humans landed on the moon for the first time. Now, many other countries want to go there as well. Why?

    The moon has a lot of minerals (矿物质) and other useful things. We want to find out if we can use them. The moon is our closest neighbor in space. We can use it as a rest station. Then, we can learn more about other planets far away in space.

    The moon is 3,474 kilometers in diameter (直径). It is about one-fourth the size of Earth. If Earth is the size of a basketball, the moon is the size of a tennis ball.

    The moon has much less gravity than Earth. If you can jump 1.5 meters on Earth, you can jump 9 meters on the moon.

    The moon is very quiet. There is no sound there. There are a lot of grey rocks on it. The moon's sky is always black.

    Our moon is about 384,400 kilometers away from Earth. The total length of the Great Wall is about 21,200 kilometers. We would have to put about ____ Great Walls end to end to reach the moon!

    A dog can't speak any words, but it can "talk". It has feelings just as you do.

    Sometime it may feel angry or afraid. Watch a dog closely, and you can find out how it feels. You can see what it is trying to tell you. When you are afraid, you may look down. When a dog is afraid, it may run away. When you are angry with other people, you stare at them. An angry dog also stares. Sometimes the hair along its back stands up.

    Do you feel guilty(有罪) when you do something you shouldn't do? Dogs can feel guilty, too. Sometimes when l come home, my dog gives me a guilty look. Then I know he did something wrong. Dogs need love and care. Some dogs are very unhappy when they are alone for a long time. Some dogs even snap(撕咬）if they don't get enough care.

    You may have a dog or you may know a dog. Take care of it well if you want to have fun with it. Take it for a walk. Don't make it do too many things. Try not to punish it again and again for doing the same thing. Always remember, a dog has needs and feelings just as you do. Talk to a dog, and it will talk to you.

    When on the go or traveling, a Disposable(一次性) Toothbrush might be just the product for you, Typically, a Disposable Toothbrush is made out of a plastic material, with toothpaste already on the brush head. Just add water while you are using it. In some new Disposable Toothbrush models, the toothpaste comes automatically(自动地) as you squeeze (挤) the handle of the toothbrush.

    Colgate has upped the competition in the Disposable Toothbrush market by creating a Disposable Toothbrush that you can use at your desk at work, in your car, or after eating at a restaurant. This toothbrush is called the Colgate Wisp, and is about the size of an index finger. The toothbrush can get to those places that are hard to reach just like a regular toothbrush. No water is necessary when using this toothbrush, making it very useful and convenient. A pack of four of the Colgate Wisp's run at about $2.99. If you are one of those people that like to brush your teeth throughout the day but hate the hassle of carrying a toothbrush and toothpaste around, this is perfect!

    Gadgets.boingboing.net is a website that allows different people to share their thoughts and experiences on a certain product. The website gives a general review on the Colgate Wisp，and following the review, people are able to share their first-hand feelings with readers. This is helpful if you are interested in purchasing the Wisp. Visit their website here: gadgets.boingboing.net.

    However, people throw them away after using them only once. It is a kind of waste and is very bad for the environment. If you travel to Beijing， remember to bring your own things. Starting from June, some hotels in Beijing will no longer provide guests with these disposable goods.