Many animals do strange things before an earthquake．This news may be important．

    Earthquakes can kill people and knock down houses．Animals may help to save lives．

    Some animals make a lot of noise before an earthquake．Farmers know about this．Dogs that are usually quiet start to bark．Horses on farms run around in circles．Mice leave their holes and run away．Cows give 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 noise．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 way is to watch the animals．

    Trees are one of the oldest " citizens (公民) " of our Earth. They keep our air clean, reduce noise pollution, improve water quality and provide food and building materials.

    Just like us, trees change a lot as they grow. At 1 to 3 years old, young trees learn how to protect themselves. For example, many trees grow thorns( 刺) to warn animals not to go near. Most young trees have large, deep green leaves so that they can catch enough sunlight and change it into their food and energy.

    When trees are 4 years old, they begin to grow very rapidly and become strong enough to face challenges later in life. At the age of 15, trees become young adults. They grow more slowly and begin to produce flowers and fruit.

    It is not until the tree is 20 to 25 years old that it becomes a real adult. The tree reaches its largest size. The adult tree gives us shade, oxygen and natural beauty; it is also a great place for a tree house, or a place for us to read a book, listen to music and so on. If we give the adult tree proper care, it will go on to live healthily for many years.

    Gradually, trees begin to grow older and older and even die. At this time, they still have their important place in nature. When a tree becomes hollow (空心的) or part of it becomes dead, it provides a home to small animals and is a source of food for many other animals.

    In many ways, the life of a tree is similar to our own life experience. When we are looking at the life of a tree, we learn about that each period of life brings its own form of joy and challenge.

    Enjoy every minute of the life of the trees and take care of the trees!

    June 5th is World Environment Day. This makes us pay more attention to our environment. When Wang Boxuan, a Beijing high school student, uses up his exercise books, he does not throw them away. Each one is kept at his school with hundreds of exercise books that are given by other students. Then they are sold to a Beijing paper-making factory.

    The paper is recycled and used again by students and teachers in the school. At the same time, the money that is made from the sales goes to schools in Inner Mongolia(内蒙古). The government there uses the money to plant more trees and grass. This place is one of the sources(源头)of the sandstorms(沙尘暴)that often attack Beijing during springtime.

    Wang's school is one of the schools in the capital that take part in the \"green promise" environmental protection activity. So far, nearly210，000 students have taken part in the activity, collecting more than 87 tons of waste paper.

    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."