Do you know why different animals or pests have their special colors? Colors in them seem to be mainly used to protect themselves.

Some birds like eating locusts (蝗虫), but birds cannot easily catch them. Why? It is because locusts change their colors with the change of the colors of crops. When crops are green, locusts look green. But as the harvest time comes, locusts change into the same brown color as crops have. Some other pests whose colors are different form plants are easily found and eaten by others. So they have to hide themselves for lives and appear only at night.

    If you study the animals' life, you'll find the main use of colors is to protect themselves. Bears, lions and other animals move quietly through forests. They cannot be easily seen by hunters because their colors are much like the trees.

    Colors are useful not only on the land, but also in the sea. A kind of fish in the sea can give out a kind of black liquid (液体) when the fish face danger. The liquid spreads over quickly, so they cannot be found by their enemies and can quickly swim away. That is why they live safely though they are not strong at all.

    Napoga is a girl in Ghana, Africa. It is hard for her family to get clean water. Every morning, she leaves home at half past five to get clean water for her family in a village far away. It takes her six hours to get enough clean water for daily cooking and drinking. She has no time to go to school or to play with her friends. Millions of people in the world are like Napoga. They can't get enough clean water to keep healthy.

    Earth Day is on April 22. But on all the other days, we must also remember it. The water we use is the most important natural resource on the Earth. Water covers about 75% of the Earth's surface. But most of that is sea water. We can't use it for many things. Fresh water covers only less than 1% of the Earth's surface.

    You probably feel lucky that your life isn't as hard as Napoga's. But that doesn't mean you don't have to worry about water. We all face serious water problems. One of them is water pollution Lots of kinds of things from cars, factories, farms and homes make our rivers, lakes and seas dirty. Polluted water is very bad for people to drink. And dirty water is bad for fish too. Now, 34% of all kinds of fishes are dying out. Scientists say that in 30 years, more than half of the people in the world won't have enough clean water. We have to learn how to save more water for ourselves and our children.

    Stop reading for a minute and think about what you see when you look up at the sky on a clear night. You probably see many stars(星星). Long long ago, farmers watch some stars to know when to plant their crops. Travellers did so to find their way in the dark. Today stars are still important to some people.

    Scientists find that most stars are very big. In fact some stars are so far away that it would take millions of years to get to them even by spaceship.

    Another thing we know today about stars is that some are made up of(由……组成) hot gases. The gases are so hot that they send out light. If you watch a star carefully, you may notice that it twinkles(闪烁) sometimes. As you may understand, light from a star must shine through the air before you can see the star. Air is always moving, it makes light from the star move back and forth. When the light moves, it makes the star twinkle. Stars also have different colours. The colours of a star depend on how hot it is. To our surprise, the cool stars are red and the hottest stars are white.

    Every day there is less and less space on Earth for rubbish. Yet every day we make more and more rubbish. What can we do? We can recycle some of our rubbish. Recycling means that the rubbish will be made into something that can be used again.

    Recycling helps Earth. And it saves space in rubbish dumps. Half of everything that we put into landfills could be recycled instead. In fact, most things made of paper, metal, glass and plastic can be recycled.

    Paper can be broken into small pieces and made into new paper. Steel and aluminum cans(金属雄)can be melted down(熔化)and made into new cans. The same is true of glass bottles. This can be done over and over again. Recycling doesn't take as much energy as making these things the first time. So we can use less of Earth's fuel resources.

    Plastic can be melted down, too. Then it can be formed into park benches, playgrounds and so on. Some people call plastic the "wood" of the future. Things made of plastic will last about 400 years-even if they stay outside in the weather. No wood can do that!

    People in Western countries are eating less meat these days, whether for their health or because they want to protect animals. But now they have another reason.

    Eating less meat can help to prevent climate change, according to a recent study published in Nature.

    Raising livestock (家畜) is bad for the environment. When animals like cows digest (消化) food, their stomachs make greenhouse gases, which are a major cause of global warming. Seventeen percent of greenhouse gas emissions (排放) come from livestock farming, The New York Times reported.

    In addition, to raise these livestock, people have to cut down forests and turn them into farms. Forests play a key role in fighting global warming because they absorb greenhouse gases.

    Eating less meat according to certain guidelines could cut global food-related emissions by nearly a third by 2050, the study found. Maintaining (保持) a vegetarian diet in the long term could bring down emissions by 63 percent.

    But eating less meat won't be easy. According to the study, people in Western countries will need to eat 90 percent less meat than they do now in order to have an impact (影响) on our climate. Scientists are now trying to find new foods to replace meat.

    Some say that insects (昆虫) could help. A 2013 UN report said that eating insects is healthier and better for the environment. They produce 75 percent less greenhouse gases than livestock.

    Some experts are creating lab-grown meat. They make meat in a lab using livestock cells (细胞). In March, US company JUST said people in the US might be able to buy its lab-grown meat by the end of this year.