When you hear about trees cut for paper, you might think of your favorite trees in the backyard, nearby parks or wild forests being cut to pieces.

 The good news is that production and use of paper will not cause forests to disappear. Most trees used for paper come from timberlands(林地). People plant trees here for use. It usually takes 10 to 20 years for trees to grow big enough to be cut down. During that time, trees provide a home for animals and produce oxygen(氧气) for the earth. And after people cut down the big trees, they plant small ones again.

 Often, a tree is not cut down for making paper at all. People use the big part for buildings. Paper is then made from the left small part.

 We also recycle paper—People collect used paper and turn it into new products, likes boxes, newsprint and writing paper, in the factory. So it's important for us to recycle paper and reduce(减少) the amount(数量) of it in landfills(垃圾处理场).

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When settlers (移民）came to America during the 1600s, they were surprised to find so many trees. Some trees were so huge that a large man could not put his arms around them. Those trees helped the settlers a lot. They were glad and thankful to have these trees. They used them to build houses and make fire. From the wood of the trees, they made furniture, tools and so on.

Most people thought the forests would last forever. However, by 1800, America had its first wood shortage (短缺). How did it happen? People had not known that trees were being cut down faster than new ones could grow.

Some American people made trips to foreign countries. There they saw destroyed forests and learnt the importance of protecting forests. They came back to the United States and warned that if Americans didn't use trees more carefully and wisely, someday the forests would all be gone. However, people were not ready to listen. Years went by, and America's forests kept disappearing. It made some people really worried. But they did nothing.

Finally, J. Sterling Morton, the man who is remembered as the father of Arbor Day (过节), got people to listen. He named a Tree-Planting Day, or Arbor Day. He worked hard to make Arbor Day a national holiday. On that day, people usually plant a lot of trees.

Today, millions of trees have been planted in the United States because of Arbor Day. Arbor Day is such a good idea that many other countries now also have Arbor Day. Many, many trees are being planted all over the world because of J. Sterling Morton's work.

    Many animals do strange things before an earthquake. This news may be important. Earthquakes can kill people and knock down homes. The animals may help to save lives.

    Some animals make a lot of noise before an earthquake. Farmers have told about this. Dogs that are usually quiet have started to bark (吠). Horses on farms have run around in circles. Mice have left their holes and run away. Cows have given less milk.

    In a town in Italy, cats raced down the street in a group. That happened only a few hours before an earthquake. In San Francisco, a man kept tiny pet frogs. One Sunday, the frogs jumped around more than ever. They made loud noises, like bigger frogs. That night, an earthquake struck the city.

    People want to know when an earthquake is coming. Then they could get away safely. Right now, there is no sure way to know ahead of time. Maybe the best idea is watching the animals.

    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.