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    Have you ever had dreams about building a robot? Or putting together a spaceship? Or even seeing your face made out of chocolate? Done. All you need is a 3-D printer.

    The possibilities of 3-D printing seem endless(无穷尽的）.All the user has to do is to design an object on the computer and choose a material to print in. The printers print in hundreds of different materials including glass, sugar and even skin! When the user presses(按）“print", the 3-D printer spreads the materials layer(层）by layer and like magic the object is produced.

    The first 3-D printer was invented in 1986 by an American, Charles Hull. But 3-D printing has only become cheap enough recently for most people to use. Designers now use 3-D printing to create unusual things. The Dutch artist Dirk Vander Kooj prints furniture made from old fridges. And doctors have used 3-D printing to print human body parts! The Telegraph reported in February that scientists from Cornell Medical College even printed a man-made ear.

    But like a lot of new technologies, if 3-D printing gets into the wrong hands, it can be dangerous.

    In 2011 a group of four men in the US used 3-D printing to produce ATM skimmers(提款机盗刷器).These were placed on an ATM and stole over $400,000 from users of the ATM. It is terrible to think that criminals like them might one day use a 3-D printer to print a gun.

    But for better or for worse, 3-D printing has been put into use. In a few years, you'll probably be wondering how you could ever live without your 3-D printer!

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    27 world records were broken during the 2016 Summer Olympics. They fell in swimming running weightlifting and a number of other sports. But how do athletes continue to get better, jump longer, run or swim faster? Although scientists say that athletes have reached their limits (极限), records continue to fall. In almost every sport, athletes have become better since the Olympic Games begin.

    One reason is that and more people than ever before have access to sports and exercise. They start at an earlier age and can compete longer in their sport. In schools more and more natural talents can be discovered.

    Besides, athletes can train full-time instead of training after works. As medicine improves, athletes can stay in competition for a longer time and overcome injuries (损伤) faster. Many top athletes achieve their best results later on in their careers. Technology has also helped improve scores.

    One of the most important reasons, however, is the human mind. We always want to be better and faster that someone else. It can release (释放) great power in our body.

    So, where are limits? One of the most difficult questions to answer is how fast a human being can run. Many years ago, nobody thought a person could ever run within 10 seconds in the 100-metre race. But the record was broken at the 1968 Mexico City Olympics. A t the moment Sustain Bolt is the fastest man on Earth at 9.58 seconds. Scientists say that 9.48 may be the limit, but, who knows, maybe some runners will one day run within 9 seconds.

    Light and shadow（影子）are friends. They usually go together. We receive light every day. At the same time, we produce shadow.

    Light cannot shine through you. Your body stops it from passing. There is a dark spot on the ground next to you. The light cannot reach the dark spot. This is your shadow.

    At noon the Sun shines over your head. Your body stops very little light from reaching the ground.

    We love light, especially sunlight. Without sunlight, life on the Earth is impossible. Most of us like to stand in the shadow of a tree in summer. But some people are afraid of their own shadow at night. They do not want to walk in a dark street. They do not want to see the shadow either. But still light and shadow usually go together.

    Around the world, there are about 7,000 National Parks. Most of them cover huge areas of land where nobody lives. However, the National Parks in England include places where people live and work, as well as wild areas where there are few human activities.

    The National Parks in England are called "England's Breathing Spaces" because they are places where people can go to be in the open air, away from the dirt and noise of cities. They provide wonderful scenes of mountains, woods, grasslands and wetlands. And there are plenty of activities to do in all of the National Parks in England. Visitors can walk or ride bikes for fun. Many of the parks put on activities for families.

    Every year there are about 110 million visitors to the parks, bringing many benefits(益处) to the areas. At the same time, it creates problems, too.

    First, life can be difficult for local people. Car parks and roads are too crowded. Gift shops and cafes take the place of many everyday shops. Even house prices in some areas can become too high. Besides, country roads can be damaged, for too many people walk, cycle or ride horses on them. Roads can be rebuilt, but then they look less natural. Another big problem to the National Parks is litter. In the parks it is a danger to wild animals. Broken glass can also cause fires by focusing the rays of the sun. Such fires in wild places can be out of control.

    _______All National Parks in England are making more rules, which tell people how to take good care of their environment. If these rules are followed, the National Parks will be well kept and continue to give pleasure to many people for a very long time.