Which animal do you think is "the king of the animals", the elephant, the lion or the tiger? They are all large and strong. But I think the tiger is "the king of the animals". If you watch carefully, you can find some black lines on the tiger's forehead(前额). The lines look like the Chinese word "WANG". The word means "the king of the world" in Chinese.
   Most of the tigers come from China and India. Tigers are dangerous animals. They look scary(吓人的). They like eating meat. They have yellow fur with black lines. They usually weigh about 200 to 300kg. Tigers can run fast. They run at a speed of 20 meters per second.
Some people think they are dangerous. But they don't know tigers are in danger now. There are only 20 to 30 wild South China Tigers in China and less than 300 in the world. Lots of people kill them for their fur. We should take action to protect them.

    In nature，you may see many insects and animals of different colors．Have you ever wondered why?

Locusts(蝗虫)are super delicious food for birds，but it is not always an easy job for birds to catch them．It is neither because locusts are good jumpers or runners nor because they are smarter than their enemies．The reason is that the colors of locusts change with the colors of crops(农作物)．When crops are young，locusts look green．But when autumn comes，locusts change to the yellow and brown color as crops do．

    Brown bears，tigers and other animals move quietly through forests．They can't be seen easily by their enemies．This is because they have colors similar to the trees．For the same reason．polar bears that live on a land of snow and ice are white．Butterflies and bees living among the flowers are colorful like flowers．Soil insects are mostly dark—colored and they live under the soil in a dark and wet environment．However，insects with colors different from plants can easily be found and eaten by others．So in order to survive ， they have to hide themselves in the daytime and appear only at night．

    Have you ever noticed some even stranger acts? The ink fish in the sea can send out some very black ink when it faces danger．As the ink spreads over．its enemies will not find themselves suddenly in a dark world．At the same time the ink fish immediately swims away．That is how it keeps itself save though it is not strong at all．

    In earliest times, men considered lightning to be one of the great mysteries (神秘的事物) of nature. Some ancient peoples believed that lightning and thunder were the weapons (武器) of the gods.

    In reality, lightning is a flow of electricity formed high above the earth. A single flash of lightning 1.6 kilometres long has enough electricity to light one million light bulbs (灯泡).

    The American scientist and statesman, Benjamin Franklin, was the first to show the connection between electricity and lightning in 1752. In the same year he also built the first lightning rod (避雷针). This device (装置物) protects buildings from being damaged by lightning.

    Modern science has discovered that one stroke (闪击) of lightning has a voltage (电压) of more than 15 million volts (伏特). A flash of lightning between a cloud and the earth may be as long as 13 kilometers, and travel at a speed of 30 million meters per second.

    Scientists judge that there are about 2,000 million flashes of lightning per year. Lightning hits the Empire State Building in New York City 30 to 48 times a year. In the United States alone it kills an average (平均数) of one person every day.

    The safest place to be in case of an electrical storm is in a closed car. Outside, one should go to low ground and not get under trees. Also, one should stay out of water and away from metal fences. Inside a house, people should avoid open doorways and windows and not touch wires or metal things.

    With lightning, it is better to be safe than sorry?

    Waste can be seen everywhere in the school. Some students ask for more food than they can eat and others often forget to turn off the lights when they leave the classroom. They say they can afford these things. But I don't agree with them.

    Waste can bring a lot of problems. Although China is rich in some resources(资源), we are short of others, for example, fresh water. It is reported that we will have no coal(煤) or oil to use in 100 years. So if we go on wasting our resources, what can we use in the future and where can we move? Think about it. I think we should say no to the students who waste things every day. Everybody should stop wasting as soon as possible.

    In our everyday life, we can do many things to prevent waste from happening, for example, turn off the water taps when we finish washing, turn off the lights when we leave the classroom, try not to order more food than we need, and so on. Little by little, everything will be changed. Waste can be stopped one day, if we do our best.

    Thanks to the Earth, we have fresh air to breathe, clean water to drink and warm sunshine to enjoy. But it seems that we haven't realized that the Earth is facing many environmental challenges and it is getting "sick".

    Scientists say that of all the environmental challenges, climate (气候) change is the biggest one. The temperature on the Earth has risen by more than 0. 5C since 1992. Cities like Singapore and Tokyo that are at low altitudes (海拔) may be covered by the ocean (海洋) in the future.

    But this is not the only problem people are facing. Since 1992, the human population has grown by 2 billion, while the population of all other animals has dropped by nearly 30 percent. At the same time, water pollution has become serious. We are also facing problems like light pollution, noise pollution and some other pollution.

    However, we have made some progress in saving the Earth. For example, we stop using harmful materials to make the hole in the ozone layer (臭氧层) smaller to slow the rise of the temperature. We do a lot of work to help the animals in danger, or more than two-thirds of the worlds wild animals may disappear (消失) by the end of 2020.

    "The progress shows that we can make good changes when we act wisely, "scientists say, "we must take action to protect the environment, or it will be worse."

Why does the sky change colors?

    What is the sky? How high is it? What color is it? What birds can live above it? These questions are difficult to answer, aren't they?

    In fact, the sky has no color. Then why does the sky look blue?

    We know that there is air around the world. When planes fly, they need air to lift their wings. Planes can't fly very high. That is because the air gets thinner when they go higher. The same will happen to us if we go high enough. If we go up about 1, 200 kilometers from the earth, we'll find no air there. Some birds can fly into the sky as high as a plane, but they cannot fly or live without air.

    Looking up above us, you will see the blue sky with white clouds. It is usually light blue. The color would be bluer when you see on the top of a high mountain. And you will see fewer clouds in the sky between you and the sun.

    Sometimes the sky doesn't look blue. When the sun rises and falls, you will see red, orange, and other colors in the sky. Such are the most beautiful moments of the day.

    Who can see the colors of the sky high above the earth? The astronauts! They can see those beautiful colors of the sky from the outer space. However, before flying into outer space, they sit in a spaceship high above the earth, and there is no air at all. The sky would be that dark and its color would be black.

    Now you may understand that we see colors because the air scatters(使散射) the sunlight. light travels through the air. Without air, there would be no light or colors.