John and Jack met at the old bench every afternoon. Then they played football. But they didn't have enough money to buy a real football. So Jack made a ball out of old socks covered with a piece of plastic. Every time, the two friends didn't stop kicking and running until very late.

    On Monday afternoon, John and Jack met again at the old bench. Soon the home-made ball was running across the grass. The boys laughed and shouted happily. The ball was stopped by a boy wearing a nice pair of sports shoes. John was upset when he saw it was Steven.

    The next morning, John's mother gave him a bill. “Your uncle sent you a birthday present.”She smiled. John's eyes grew big when he saw the ＄100 bill. Later that day, his mother bought a pair of new sports shoes and a real football.

    That afternoon Steven invited John to play football. Steven did not want Jack to join them only because Jack's sports shoes were dirty. When the game was over, John and Steven walked past the old bench where Jack was sitting. Steven picked up a stone and threw it at him. John, holding his new football in his hands, walked on and did not look back.

    Several days later, as John walked past the old bench, he saw something lying under it. He looked closer and saw it was the home-made ball. John was full of sadness when he saw the ball. As his sadness turned to anger, he picked up his new football and kicked it into the air. Then he walked to the beach, sat down and waited.

    In 1901, H. G. Wells, an English writer, wrote a book describing a trip to the moon. When the explorers (探险者) landed on the moon, they discovered that the moon was full of underground cities. They expressed their surprise to the "moon people" they met. In mm, the "moon people" expressed their surprise. "Why are you travelling to outer space when you don't even use your inner space?" they asked.

    H. G. Wells could only imagine the travel to the moon. In 1969, human beings really did land on the moon. People today know that there are no underground cities on the moon. However, the question that the "moon people" asked is still an interesting one. A growing number of scientists are seriously thinking about it.

    Underground systems (体系) are already in place. Many cities have underground car parks. In some cities, such as Tokyo, Seoul and Montreal, there are large underground shopping areas. The "Chunnel", a tunnel connecting England and France, is now completed.

    But what about underground cities? Japan's Taisei Corporation is designing a network of underground systems, called "Alice Cities". The designers imagine using surface space for public parks and using underground space for flats, offices, shopping and so on. A solar dome (太阳能穹顶) would cover the whole city.Supporters of underground development say that building down rather than building up is a good way to use the earth's space. The surface, they say, can be used for farms, parks, gardens, and wilderness. H. G. Wells's "moon people" would agree. Would you?

Why salmon will newer get lost

    When you're packing for an adventure, what's the most important thing you'll need? If you don't want to get lost, you' need a map. Or better yet, a GPS. What about other animals? How do they know where they're going?

    While humans depend on technology to travel, some animals have something far more advanced. Researchers, mainly from Oregon State University, US, found that Chinook salmon have a "built in GPS" of the Earth's magnetic field(磁场). This means as soon as they are born they are able to direct themselves in the ocean. It acts like a big map inside their brain.

    Scientists placed some baby salmon into a big swimming pool. To simulate the Earth's magnetic field, they put magnetic coils(线圈) all around the pool. Then, by changing the direction of the coils, the salmon began to change their own direction. They started to face in the direction of their ocean feeding area. This is a safe place in the ocean where salmon can find food to eat. When the scientists changed the coils to the opposite side, the salmon also turned in the opposite direction. Just by using their "built-in GPS", the salmon were able to figure out the direction of their feeding area.

    How did Chinook salmon get their "built in GPS"? The scientists believe that their navigation(导航) skills came through evolution(进化). The fish that were able to reach the feeding area lived longer. Then they could pass on their navigation skills to their babies. So if you're ever lost and in need of some help, maybe you should ask a salmon to point you in the right direction!

    Artificial intelligence(AI)(人工智能)is the ability of a computer program or a machine. The computer or the machine with AI can think and learn. It is also a field of study that tries to make computers "smart". John McCarthy, a scientist, came up with(提出)the name "artificial intelligence" over 60 years ago. Many things such as learning and problem solving can be done by computers, though not in the same way as people do.

    An unusual goal of AI research is to create computer programs. They can learn, solve problems, and think logically(逻辑地). At present, Al can successfully understanding human speech, recognizie (识别)human faces, operate self-driving cars and compete in some game systems like playing Chess. However, Some people also consider(认为）AI a danger to humans if it develops too quickly. A famous British scientist also was not for this kind of technology.

    Math is the basic language of AI. If students are good at math, they will be more likely to become successful AI designers(设计者)in the future. We need not only bright students, but also average(普通的)students. As for(对于)average students ，if they get enough math skills, they can also become successful AI designers. Besides, a good knowledge of computer science is also necessary for AI designing.

    Scientists hope to create creative(有创造力)and emotional (有感情的)AI. The AI can possibly understand human feelings or create art. Many ways and tools have been tried to discover this wide and exciting field.