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!

    Have you ever heard robot fish? Scientists will put some robot fish into the sea near Spain. These robot fish will help people to detect (探测) the pollution in the water. If the robot fish are able to finish their work successfully, the scientists hope to put them into rivers, lakes and seas around the world.

    The fish are about 1.5 meters long. There will be a detector in their bodies. They can find the sources (来源) of pollution in the water, and then the robot fish will eat part of it. Unlike other robots, they don't need to be controlled by people far away. The robot fish all have an eight-hour battery (电池). They can "swim" in the sea freely and send back information to people on the beach. After their batteries die, they will return by themselves.

    There are five robot fish altogether now. Each costs about 29,000 dollars. They are part of a three-year project between engineering company BMT Group and Essex University in southeastern England.

    "We invented the robot fish creatively. We hope them can find the changes in the sea water and report back the information," said Professor Hu of Essex University. His team is developing the fish.

    Since the first person walked on the moon in 1969, technology has greatly helped space exploration. In recent years scientists have built a special robot to accompany astronauts on space missions (任务). Because this robot looks and moves like a person, scientists call it a humanoid robot. The latest model of the humanoid robot is known as R2, short for Robonaut 2.

    R2 was first launched into space on February 24, 2011. It was built by the National Aeronautics and Space Administration (NASA) and the car producer General Motors (GM).

    R2 weighs 330 pounds and costs $2.5 million to build. It has arms and a head- filled with vision equipment—but no legs. Its "brain", or computer, is in its stomach. R2's arms can hold 20 pounds. Each bendable finger has 5 pounds of grasping force. R2's hands are also skillful. Since its hands are shaped like human hands, R2 can use human tools to complete tasks traditionally performed by astronauts." Astronauts absolutely have their day packed from the minute they wake up until they go to bed. If Robonaut can provide just an hour's worth of relief to the astronauts doing something they don't want to do, that would make it worth it right there," says Nic Radford, the deputy project manager of R2.

    One advantage of working with R2 will be that ii can't complain about its work! Astronauts will also appreciate the fact that the robot can perform its duties without constant supervision (监管). R2 can be assigned a task and then checked on periodically. If R2 does not complete a task correctly, astronauts will be able to make minor adjustments to adapt (适应) the robot's behavior so that the task gets done right.

    R2 is still in the design stage of development, which means that scientists are frequently testing it and looking for ways to improve it. Right now, humanoid robots do not have the protective equipment needed to work outside the space station. As technology advances, humanoid robots will be able to help astronauts with dangerous tasks as well as routine ones.

    In the future, humanoid robots will be astronauts' eyes in space, going to places considered too difficult or unsafe for astronauts to explore. Some of them will be mounted on wheels to explore the surface of planets or asteroids (小行星). The robots will be able to send back videos and help astronauts gather information about the atmospheres of these places.

    One outcome of using these humanoid robots will be a greater understanding of the interaction between humans and robots. NASA engineers believe that when humans and robots combine forces and work together, the results will be better than what either could achieve alone. John Olson, a director at NASA headquarters in Washington, D.C, says that the project will allow us to go farther and achieve more than we can probably even imagine today.

    Why do we like drinking water from plastic bottles? Some people think it is healthy and clean. Others drink bottled water because it's easy—you can carry it around with you. In hot countries, like Greece, we often buy bottles of cold water in summer.

    However, making lots of plastic is not a good idea for many reasons. First of all, we need a lot of oil for plastic products. We usually use oil as a source(资源) of energy. If we reduced the number of bottles we made, we wouldn't need so much oil. Plastic bottles also pollute the environment. If we recycled all our plastic bottles, we wouldn't need so much space for rubbish dumps. But in Greece, we don't recycle much of the plastic we use. In 2006, Greeks recycled only about 10% of plastic waste. The rest became rubbish on land and in rivers and seas.

    So next time you want to throw away a plastic bottle in the litter bin, stop and think. If you recycled it, you would help the environment. But what can you do when there isn't a recycling bin near you? Well, there are lots of useful ways that you can use your bottles again. For example, an empty bottle makes a great piggy bank for your pocket money, and if you cut a bottle in half, you will have a plant pot. Go green! You can make a difference.

    Owls live in almost every country in the world. Most owls don't sleep at night. When they fly, you can't hear them. They are very quiet. Owls are good at hunting（捕猎）. They eat a lot of things such as mice, snakes, small birds and even fish. Owls have very good hearing. That helps them to hunt well in dark places. Their eyes are special. Both of their eyes face front. They can see very far away. There are facial disks(面盘) around their eyes. These facial disks can help with their hearing. Owls can turn their heads 270°. That helps them see what's going on all around them.

    Maybe because owls look a little different and have special life habits. There are a lot of stories about them. Some cultures believe that owls are very clever and some cultures think owls may bring bad luck to people. In fact, owls are really good friends of people. They eat lots of mice every year. That helps save a lot of food for people. But the number of owls in the world is becoming smaller and smaller because of people's activities. Now owls are protected by law(法律) in many places of the world. For example, in some places, people can't keep an owl as a pet at home.