Forests have always been useful and important to men who make use of them in many ways. Every day trees are serving man everywhere. Trees supply man with fruits and building materials in the form of wood. Without trees it would be impossible to build houses, boats, bridges and so on. Furniture such as desks, chairs and beds is made of wood. Trees can stop man from the terrible heat. They're also useful in preventing(阻止) good and rich top soil from being washed away during heavy rains. If there were no forests, heavy rains would wash away the rich surface(表层) soil that is so important to plants. The result is that the land will become a desert. There are plenty of desert areas in the world. A long time ago these desert areas used to be very rich areas, but men in the past had no enough knowledge about science of nature, and they cut down too many trees in the area where they lived and never planted new ones. By and by, the rich surface soil was blown and washed away by strong winds and heavy rains. In the end the rich land changed into useless deserts where nothing could grow.

    One day, Mr. Arnold was teaching a lesson, and things were going as normally as ever. He was explaining the story of human being to his pupils. He told them that, in the beginning, men were nomads (游牧); they never stayed in the same place for very long. Instead, they would travel about, here and there, in search of food, wherever it was to be found. And when the food ran out, they would move off somewhere else.

    He taught them about the invention of farming and keeping animals. This was an important discovery, because by learning to cultivate (耕作) the land, and care for animals, mankind would always have food steadily. It also meant that people could remain living in one place, and this made it easier to set about tasks that would take a long while to finish, like building towns, cities, and all that were in them. All the children were listening attracted by this story, until Lucy jumped up:

    "And if that was so important and improved everything so much, why are we nomads all over again, Mr. Arnold?"

    Mr. Arnold didn't know what to say. Lucy was a very clever girl. He knew that she lived with her parents in a house, so she must know that her family were not nomads; so what did she mean?

    "We have all become nomads again,” continued Lucy, " The other day, outside the city, they were cutting the forest down. A while ago a fisherman told me how they fish. It's the same with everyone: when there's no more forest left, the foresters go elsewhere, and when the fish run out, the fishermen move on. That's what the nomads did, isn't it?

    The teacher nodded, thoughtfully. Really, Lucy was right. Mankind had turned into nomads. Instead of looking after the land in a way that we could be sure it would keep supplying our needs, we kept developing it until the land was bare. And then off we would go to the next place! The class spent the rest of the afternoon talking about what they could do to show how to be more civilized (文明的).

    The next day everyone attended class wearing a green T-shirt, with a message that said "I am not a nomad!"

    And, from then on, they set about showing that indeed they were not. Every time they knew they needed something, they made sure that they would get it using care and control. If they needed wood or paper, they would make sure that they got the recycled kind. They ordered their fish from fish farms, making sure that the fish they received were not too young and too small. They only used animals that were well cared for, and brought up on farms.

    And so, from their little town, those children managed to give up being nomads again, just as prehistoric men had done, so many thousands of years ago.

    Australia's Great Barrier Reef(礁) is the world's largest reef system. It is over 2,600 kilometers long. The reef is home to many animals: fish, birds, turtles, sharks and even whales. Unfortunately, the reef that all these animals call home is in danger.

    Climate(气候)change, over fishing and water pollution are damaging(毁坏)the reef every year. Coral(珊瑚)reef experts at Australian universities say that if we do nothing to stop it, the coral reef could be destroyed before the year 2030.

    Everyday things like driving cars, using electricity and running a factory give out greenhouse gases into the air. These gases make Earth warmer and warmer. This is a problem for the Great Barrier Reef and other reefs around the world.

    Coral is very fragile, and even a 2-degree increase in water temperature is enough to kill it, according to Ove Hoegh-Guldberg, reef researcher at the University of Queensland, Australia. If the water temperature doesn't go down, the coral dies.

    But it's not only the coral that's in danger. One quarter of all sea life lives on coral reefs.

    If air pollution is not slowed down or stopped, then the water will warm by at least 3 degrees in the next 20 years, according to reef experts in a report from University of Queensland. This would spell the end for the Great Barrier Reef and all its sea life.

    Some people claim they" never forget a face". But what does that saying mean? Is there really no limit to the number of faces a person can remember? A new study at the University of York in England has found that, on average, people can remember as many as 5,000 faces.

    The study is the first time that scientists have been able to put a number to the abilities of humans to recognize faces. The research team tested people on how many faces they could remember from their personal lives and in the media. They also tested them to see how many famous faces they recognized. Rob Jenkins works in the psychology department at the University of York. He said the researchers' study centered on the number of faces people actually know. He said the researchers were not able to discover whether there is a limit on how many faces the brain can handle.

    In the study, people spent one hour writing down as many faces from their personal lives as possible. At first, they found it easy to come up with many faces. But by the end of the hour, they found it harder to think of new ones. Their change in speed let the researchers estimate when they would have run out of faces completely.

    The results showed that these people knew between 1,000 and 10,000 faces. Jenkins explained that some people may have a natural ability for remembering faces." There are differences in how much attention people pay to faces and how well they process the information," he said. Jenkins also said it could be because of different social environments. Some people may have grown up in more populated places. Therefore, they may have had more social contact throughout their lives.

    The people in the study included 25 men and women between 18 and 61 years old. Researchers think age may be an interesting area for further research. "It would be interesting to see whether there is a peak age for the number of faces we know", Jenkins said. He said it is possible that we gather more faces throughout our lifetime. But, he added, there also may be an age at which we start to find it harder to remember all of those faces.

    The study suggests our facial recognition abilities enable us to deal with the many different faces we see on the screens, as well as those we know, like family and friends. Today, facial recognition technology is used in many ways, including by law enforcement agencies to prevent crime and violence. Governments use it to keep secret areas secure and, in extreme cases, control populations. .Even Facebook uses facial recognition. For example, when you "tag" or name a friend, Facebook technology may recognize the person's face from a different picture you had shared before.

    Mike Myers is a teacher at Chauncey Rose High School in Terre Haute, Indiana. Last year, he taught his students about the world's rain forests. They learned that rain forests are important because the plants and animals of the rain forests give us food, wood and medicine.

    Destruction of the world's rain forests is a severe problem. As part of a class project, Myers' students bought three acres (英亩) of rain forest in Central America. They paid $25 for each acre. The students hope that the land they bought will be protected and not destroyed.

    Last June, Myers and four of his students took a boat ride down a river. They saw alligators and crocodiles. In the middle of the week, a guide took Myers and his students into the rain forest. "The monkeys were not happy that we were in their forest. They broke small branches off the trees and threw them at us," one of the students said. "It was a great journey of exploring nature for all of us," said Myers.

    Each student close something special about Costa Rica to study involving the plants animals, food, and culture. During the last few days the group had time to do fun activation. They went whitewater rafting and horseback riding, and visited Costa Rica's active volcano.

    Myers hopes to make the trip every year with a different group of kids.