The population of the Earth is growing faster. It is important that we look after the Earth. We need it!
The Earth gives us a lot of things. We also give the Earth a lot, but some of the things are not good.
In nature, when something dies, other animals and plants get food from it. Every animal or plant gives food for other animals or plants. However, animals can't get food from many of the things that we ‘give' the Earth. Animals and plants can't eat metal, plastic and glass. These things will stay in the ground for many, many years.

Some rubbish is very dangerous for plants and animals. In some places, many animals live together. One animal makes food for many more animals. If we put rubbish and chemicals in the water, the plankton(浮游生物) can die. If there isn't any plankton, many animals have nothing to eat.
So what can we do? Don't leave any rubbish in the countryside! Don't make so much rubbish!

    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. Travelers 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 colors. The colors of a star depend on how hot it is. To our surprise, the cool stars are red and the hottest stars are white.

    Researchers have developed paper that can be printed with UV light (紫外线), free from the need for ink (油墨). People can clear the information away on the light-printable paper by heating it to 120℃and it can be reused more than 80 times.

    The research was carried out in order to reduce the effects of paper production on deforestation (滥砍滥伐). The researchers, from Shandong University in China and the University of California, Riverside, said that the secret behind the technology is a color-changing chemical. A thin coating of the chemical can be used on usual paper and turn it into a reusable, light-printable one. Heating the paper for 10 minutes can help clear the information away more quickly.

    Professor Yadong Yin, a chemistry professor at the University of California and a co-author of the study, said, "The greatest importance of our work is the development of a new technology to produce an ink-free rewritable paper that has the same feel and appearance as usual paper. Our work is believed to have great economic and environmental influences on the modem society." Paper production has a bad influence on the environment. It's the main cause of industrial pollution and paper thrown away by people makes up about 40% of landfills where waste is buried under the ground.

    It is predicted that light-printable paper will be inexpensive in the future. The printing process is also more cost-effective than the usual one as no ink is needed. Most importantly, it can be reused many times, which greatly reduces the cost.

    There are millions of stars and planets in space. What's the difference between stars and planets? Stars can give out heat and light, but planets cannot.

    The sun is one of the stars. Some planets are balls of rock and some are balls of gas. We live on the planet earth. The earth spins around once every day to give us day and night. The earth goes around the sun once every year to give us different seasons.

    There are eight planets moving around the sun. We call the family of the sun and its planets the solar system. Mercury is the nearest to the sun, so it is very hot. It is the smallest planet. Venus is very bright and hot. It is the nearest to the earth. Mars is covered with orange-red desi and rocks, so it looks like a red star in the sky. It has seasons like the earth. Jupiter has more than 16 moons （卫星）and it is the biggest and heaviest planet. Saturn has more than 22 moons. The other planets, such as Uranus and Neptune, are all very far from the sun and very cold. We need a telescope（望远镜）to see them.

    Mint (薄荷) is a useful plant. You can see it in different kinds of dishes. Mint can bring us many health advantages. It can also help us relax. Don't you believe it? Just smell the plant when you feel tired.

    Now, if you love mint, you don't have to buy it at the market. The plant is very easy to grow. You can plant it all year round, and it can grow well both indoors and outdoors.

    ①Prepare your flower pot (盆)

    Fill your flower pot with soil. Fill soil to a depth (深度) of about 25 centimeters. Use a garden fork to loosen the soil (松土).

    ②Plant your mint

    Plant your mint seeds (种子) 40 centimeters far from each other. If your pot is small, use just one plant or seed.

    ③Put your plant in a proper place

    Mint loves sunlight, but it also likes a bit of shade. Put your plant in a place where it can get both sunlight and shade.

    ④Water your mint

    Mint prefers wet soil. Keep the soil well watered, but don't overdo it. Don't forget to put a plant plate under your pot.

    ⑤Time to harvest

    Mint grows fast. After your plant grows up, you can pick its leaves at any time.

    To make things more fun, why not ask each of your classmates to grow some mint? Let's see whose mint grows the fastest!