In London's art gallery six or seven men, mostly in their 30s, are busy painting the walls with new designs in colorful lettering and clever tricks. Tins of spray paint and beer stand on the ground. The atmosphere is not unlike that of a golf course: a mix of concentration and relaxation.

    Graffiti(涂鸦) painting is traditionally a daring hobby. Teenagers avoid security guards to put their names on trains and buses. But over the past decade that has almost disappeared from Britain's cities. Between 2007 and 2017 the number of incidents of graffiti recorded by the British Transport Police fell by 63%. A survey by the environment ministry shows that fewer places are damaged by tags(绘名) than ever. Graffiti are increasingly limited to only a few walls. In time the practice may die out entirely.

    The most obvious reason for the decline in tagging and train-painting is better policing, says Keegan Webb, who runs The London Vandal, a graffiti blog (博客). Numerous cameras mean it is harder to get away with painting illegally. And punishments are more severe. A generational change is apparent, too. Now teenagers prefer to play with iPads and video games. Those who do get involved tend to prefer street art to graffiti. And the internet helps painters win far more attention by posting pictures online than they can by breaking into a railway yard.

    Taggers and graffiti artists mostly grew up in the 1980s and 1990s. Those men are now older and less willing to take risks. "We can't run away from the police any more," says Ben Eine, who turned from tagging to street art. The hip-hop culture that inspired graffiti in the first place has faded. Video games and comic books provide more inspiration than music.

    Graffiti may eventually disappear. But for now the hobby is almost respectable. Mr Eine says he has lots of friends who used to paint trains. Now with wives and children, they paint abandoned houses at the weekend. It has become something to do on a Sunday afternoon—a slightly healthier alternative to sitting watching the football.

    There is no doubt that many parents want to mold (塑造)their child to be better, faster, smarter and more skilled. Even though human parents can't do that, a robot that builds its own children can. Scientists at the University of Cambridge in England have created a mother robot that not only creates its own children, but tests out their performance.

    The mother robot analyzes(分析)the performance of each of the “children” it creates, and passes down good characters to the next generation

    For example, as the mother creates them and puts them to work, she measures how they're behaving, and she uses data from this behavior to create the next generation of robots.

    The mother robot can actually build hundreds of child robots and see the performance of these child robots. And if their performance is good, keep their design for the next generation. And if bad, just let it go.

    “We program the robots based on some functions that define(规定)the reward the robots are going to get, depending on the construction that they make. They cannot change their own reward. For the child robot, the longer the distance the robot walks, the better the reward it receives,” said Fumiya Iida, the lead researcher.

    After several generations, the “children” were running twice as fast.

    “The mother robot produced 500 robots to see which one is good and which one is bad,” said Iida.

    The researchers believe that the machines can be used in a car factory, for example, where robot cameras examine each ear in production line, find out any mistakes, and then design a better car.

    Although English is not as old as Chinese, it is spoken by many people around the world every day. English speakers are always creating new words, and we are often able to know where most words come from.

    Sometimes, however, no one may really know where a word comes from. Did you ever think about why hamburgers are called hamburgers, especially when they are not made with ham? About a hundred years ago, some men went to America from Europe. They came from a big city in Germany called Hamburger. They did not speak good English, but they ate good food. When some Americans saw them eating round pieces of beef, they asked the Germans what it was. The Germans did not understand the question and answered. "We came from Hamburger." One of these Americans owned a restaurant, and had an idea. He cooked some round pieces of beef like those which the men from Hamburger ate. Then he put each between two pieces of bread and started selling them. Such bread came to be called "hamburgers". Today "hamburgers" are sold in many countries around the world.

    Whether this story is true or not, it is certainly is interesting. Knowing why any word has a certain meaning is interesting, too. The reason, for most English words, can be found in any large English dictionary.

    Please Choose Cloud Services

    May be unsure, or you do not know where to begin. Trying every Cloud service would take a lot of time and work. But, the website Reviews.com might help.

    One valuable feature is the protection of digital files, including photos, videos, documents, music and more. If the worst happens and your computer crashes, or gets lost or damaged, your files can still found in the Cloud.

    Cloud services let you access your files from almost anywhere. No need to worry about a file stored on your computer when you are away from your desk. If you have an Internet connection, you can open your files from any computer, or from a phone, when they are stored using a Cloud service.

    Using a Cloud service makes sharing files easier. If you send documents to a group using emails, you may then wonder which version everyone is working with. When sharing files using a Cloud service, everyone will see the same document and the latest version.

    The first thing to consider is the amount of storage space you need. Check how much space you are currently using on your computer and mobile devices. If your computer or phone is filled with photos and you have little free space, you may want to move your photos to the Cloud. Some Cloud services are free. But, if you need a lot of space, you will probably need one that costs money.

    Even if everyone you have ever met is a Windows user, you still probably want a Cloud service that works with many platforms. You might become friends with an Android user or start a job with a company that computers on Apple!

    What is eBay? The simple answer is that it is a global trading platform(贸易平台) where nearly anyone can trade practically anything. People can sell and buy all kinds of products and goods, including cars, movies and DVDs, sporting goods, travel tickets, musical instruments, clothes and shoes—the list goes on and on.

    The idea came from Peter Omidyar, who was born in Paris and moved to Washington when he was still a child. At high school, he became very interested in computer programming and after graduating from Tufts University in 1988, he worked for the next few years as a computer engineer. In his free time he started eBay as a kind of hobby, at first offering the service free by word of mouth. By 1996 there was so much traffic on the website that he had to upgrade(升级) and he began charging a fee to members. Joined by a friend, Peter Skill, and in 1998 by his capable CEO, Meg Whitman, he has never looked back. EBay has gone from strength to strength. It is now one of the ten most visited online shopping websites on the Internet.

    eBay sells connections, not goods, putting buyer and seller into contact with each other. All you have to do is make an e-photo, write a description, fill out a sales form and you are in business: the world is your market place. Of course for each item sold eBay gets a percentage and that is great deal of money. Every day there are more than sixteen million items listed on eBay and eighty percent of the items are sold.

    Welcome to our school. You can do a lot of things here. Come and join us.