Have you ever wondered why birds sing? Maybe you thought that they were just happy. After all, you probably sing or whistle when you are happy.

    Some scientists believe that birds do sing some of the time just because they are happy. However, they sing most of the time for a very different reason. Their singing is actually a warning to other birds to stay out of their territory.

    Do you know what a “territory” is? A territory is an area that an animal, usually the male, claims（声称）as its own. Only he and his family are welcome there. No other families of the same species are welcome. Your yard and house are your territory where only your family and friends are welcome. If a stranger should enter your territory and threaten you, you might shout. Probably this would be enough to frighten him away.

    If so, you have actually scared the stranger away without having to fight him. A bird does the same thing. But he expects an outsider almost any time, especially at nesting（筑巢）season. So he is screaming all the time, whether he can see an outsider or not. This screaming is what we call a bird's song, and it is usually enough to keep an outsider away.

    Birds sing loudest in the spring when they are trying to attract a mate and warn others not to enter the territory of theirs.

    You can see that birds have a language of their own. Most of it has to do with attracting mates and setting up territories.

    There is a breakthrough in building aircrafts. Bendable wings covered with overlapping(部分重叠) pieces resembling fish sizes could be used to build swifter, fuel-efficient aircraft, a new study finds.

    Nowadays, conventional aircrafts typically rely on ailerons (副翼) to help control the way the planes tip as they fly. However, when the Wright brothers flew the first airplane, Flyer 1, over a century ago, they used no ailerons but wires and pulleys that twisted the wood-and-canvas wings, to control the plane.

    Scientists have long sought to develop aircrafts that can alter their wings during flight, just as birds can. However, most previous attempts have failed because they relied on heavy mechanical control structures within the wings. These structures were also complex and unreliable, said Neil Gershenfeld, a physicist and director of the Center for Bits and Atoms at Massachusetts Institute of Technology (MIT).

    The new wing consists of a system of tiny, strong, lightweight modules. The shape of the wing can be changed uniformly along its length using two small motors, which apply a twisting pressure to each wingtip. These wings are covered in “skins” of overlapping strips of flexible material resembling fish sizes. These strips move across each other as the wings alter, providing a smooth outer surface, the researchers explained.

    Wind-tunnel tests of these wings showed that they at least matched the aerodynamic properties of conventional wings, at about one-tenth the weight. Initial tests using remotely piloted aircrafts made with these wings have shown great promise, said Benjamin Jenett, a graduate student at the Center for Bits and Atoms at MIT.

    The new modular structures the scientists developed could be manufactured quickly in mass quantities and then installed by teams of small robots. These modular structures also can be disassembled more easily, making repairs simpler.

    “Still, the first aircraft built using this strategy will not be a passenger jet, ”Gershenfeld said. “Instead, the technology will likely first be tested on unmanned aircraft, leading to drones (无人机) that can fly for a long time, to help deliver internet access or medicine to remote villages and do some rescue works.”

    Have you ever been to London? Here is some hotel information for you.

    Kingsway Hall Hotel

    We offer quality service (优质服务) in Kingsway Hall Hotel. This location puts guests in easy reach of many places, such as the British Museum and Piccadilly Circus. Our hotel also has modern Western food, and offers a perfect dining environment. The lounge bar is a comfortable place to enjoy a drink while watching the tourists. There are hundreds of dining choices within walking distance. Non-smoking rooms are ready for guests.

    Hilton Docklands Riverside

    Located on the bank of the Thames, our hotel is about two miles east of Tower Bridge and 36 miles from London Heathrow Airport. Our hotel has a beauty salon, a flower shop and a swimming pool. The hotel also offers different kinds of service：laundry (洗衣店) services, babysitting, shining shoes, and local area transportation.

    Windermere Hotel

Located in the center of London, our hotel puts guests within easy reach of London's well-known buildings. Buckingham Palace and the Royal Parks are just a short walk away. Within 1.5 miles you can visit Westminster Abbey and the Houses of Parliament. The theatres, Harrods shopping centre, and the designer shops of Sloane Square and Knightsbridge are all only a short walk away or a taxi ride away.

    One of the most important things in the world is friendship. In order to have friends, you have to be a friend. But how can you be a good friend at school？

Listen﹣Listen when they are talking. Don't say anything unless they ask you a question. Sometimes it's not necessary for you to have anything to say; they just need someone to talk to about their feelings.

    Help them﹣If your friend is ever in need of something, be there to help them. You should try to put them first, but make sure you don't do everything they want you to do. Try to take an extra pencil or pen with you to classes in case they forget one. Have a little extra money in your pocket in case they forget something they need.

    Be there for them﹣Be there for your friends to help make them feel better in hard times. Marilyn Monroe, a famous U.S. actor, once said, "I often make mistakes. Sometimes I am out of control, but if you can't stay with me at my worst, you are sure not to deserve to be with me at my best." Always remember this! If you don't want to stay with your friends when they're in hard times, then you don't deserve to be with them when they're having a good time!

    Make plans﹣Try to make plans with your friends. Go shopping, go for ice cream, have a party, go to a movie and so on. Take time to know each other even better by doing something you both enjoy. By planning things together, you both can have a good time. And you'll remember these things when you're all old!

    You can tell a lot about a country by what's on its television sets. Britain's TV screens are completely steeped in class, and have long been so.

    From laughing at poor people in reality shows to laughing at posh people in Downton Abbey, this is how Britain likes to unwind in the evening: by laughing at other classes, and laughing at people for laughing about class.

    Like it or loathe it, many see the class system as a quite essential element of British life, together with our obsession for tea and cake and talking about the weather.

    Whether you are a lord, a lady, or just the king of your own middle class kingdom, everyone in the UK fits into the class system. How the class system works is a hard question even for a British person to answer.

    There are four main groups in the British class system: lower, working, middle and upper class. Although recently the BBC has tried to confuse everyone even more by adding three more categories.

    The British are very aware of class; it is often said that we have an in-built 'class radar'; we pick up on subtle social clues which indicate which class a person comes from. Class is not just about your job, where you live and how much you earn. It's about who you are.

    When he was a kid, Alex Vardakostas began working in the grill (烧烤店)alongside adult employees. He estimates he has cooked 50,000 burgers (汉堡包).

    Now, Vardakostas co-owns a burger joint called Creator, in San Francisco, California. But he doesn't stand over a grill flipping burgers, and neither do his employees. At Creator, burgers are cooked and assembled entirely by machine. And because it costs less to maintain the machine than to pay a kitchen's worth of employees, burgers cost less.

    Creator is just one example of a growing phenomenon: Automation is taking over more and more jobs. That means work is done by machines or computers instead of people.

    According to a report from McKinsey Global Institute, about 800 million people could be forced out of their jobs by 2030. McKinsey predicts that as technology improves, some tasks will be done more quickly or cheaply by machine, so businesses will install robots or computer Programs to perform them.

    Some jobs are more likely to be automated than others. Machines can do jobs that have three characteristics: They are routine, repetitive, and predictable. Some of these jobs pay low wages and require little education. But others pay well and demand an advanced college degree. Taxi drivers, cashiers, lawyers, and doctors all perform some tasks that can be done by machines.

    So what jobs are safe from automation? Answers include coming up with new ideas or work that involves interacting with other people and building relationships. Jobs in engineering, science, the arts, therapy, and nursing are examples.

    At Creator, Vardakostas hired people to do just that kind of work. Instead of repetitive burger prepping, workers interact with customers and advise them on flavor pairings, like mushroom sauce with pickles and onion jam. "In our world at Creator, all the work is creative and social," Vardakostas says. "And I think that is what we're going to see more of the future."