Language students often think they have memory problems. They worry because they can't remember words. In fact, the problem usually isn't with their memory. The problem is with how they study.

    To remember words better, you need to understand how memory works. There are two kinds of memories: short-term and long-term. When you see, hear, or read something, it goes first into short-term memory. But short-term memory lasts for only a few seconds. You will only remember something longer if it goes into long-term memory. Your long-term memory is like a very big library with many, many books. And like a library, it's organized (有条理的). When you put away a book – or memory – you can't just leave it anywhere. You have to choose a place where you can find it again.

    How can you do this with vocabulary? The answer is to work with the word and think about the word in new ways. You can do this by writing new sentences that include it. Even better, you can invent a little story about the word, with people or places that you know. Another way is to make a picture in your mind with the word. For example, if the word is height, you can think of the tallest person you know and try to guess his or her height. All of these activities are good ways to think about words. They make the meaning of words stronger in your long-term memory. And they give a way to find a word when you need it.

     With the development of the Internet, many people use it very often, including some teenagers. But many parents are worried about that their children may meet with something unhealthy online. To solve this problem, a new search engine for children named Kiddle has appeared.

     Search results are filtered, so only safe website are shown and descriptions are written in simple language. Searches with bad words are shut off, too. Kiddles uses the same color as Google in its logo and a similar design on its homepage, too— with an extra robot picture. The top three Kiddle research show safe websites and pages written specially for kids and those websites and pages are well chosen and checked by Kiddle developers. The fourth to seventh results will be safe and trusted websites that are not written for adults. They provide expert content, but are harder for kids to understand.

     Unlike on Google, most results appear along with large thumbnail pictures(缩略图) to make it easier for children to find what they are looking for. For example, when you search for “meow meow”. Google produces pages for information about a drug(毒品)，but Kiddle lists information only about cats. The company explained, “Websites which appear in Kiddle search results satisfy family–friendly requirements, as we filter websites with unhealthy content.”

    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.

    How do people find their ways? At first, people did it by looking at the sun, the moon and stars, Later, we started to use the compass(指南针).Today, there are navigation satellite systems.

    A navigation satellite system uses groups of satellites, they send information to a receiver, such as your smart phone. Then they can find where you are.

    The earliest navigation system is the Global (全球的) Positioning System(GPS) of the United States, The US has put 24 satellites into space to make sure GPS can locate a person correctly and globally. Russia's GLONASS and European Union's Galileo can also work globally.

    The BeiDou Navigation Satellite System (BDS) is China's homegrown navigation system. It was set up in 2000. With it, China became the third country to build a navigation system after the US and Russia.

    BeiDou can find you wherever you are. It helps you go faster by finding shortcuts and using correct directions. When you are in trouble and call the police, they will know exactly where you are if you have a smart phone that uses BeiDou.

    Today, there are more than 20 BeiDou satellites above our heads. And the system is able to offer open services to the Asia— Pacific area.

    China plans to send more BeiDou 3 satellites into space. BeiDou—3's position accuracy(精确度) is less than five meters, By 2020, the BeiDou system will have 35 satellites and  begin serving Globally.