When the Normans built their first simple wooden castles in England，they built them on the top of small hills.The first permanent castles were made of stone and built with thick walls.The main building was usually surrounded by walls which overlooked the moat (护城河)．

     The entrance to the castle was usually over a drawbridge (吊桥) leading to the main gatehouse.The drawbridge could be raised or lowered and an iron grille (栅栏) could be lowered to shut off the entrance to the gatehouse.

     As time went on，the castle builders became more advanced in their techniques.Instead of building a strong central building and surrounding it with walls of lesser strength，they thought out the idea of surrounding a central area with huge walls which could contain all the main rooms of the castle.These walls usually had many towers and these towers were really a series of main buildings along the castle walls.In building these castles they used hill sites whenever possible in order to give the castle a better position.Because the outside world was shut off by a barrier or curtain of defences，they are called “curtain wall” castles.

     With the passing of time there was less need to build strong castles and nobles built manor (庄园) houses.These manor houses often had battlements and iron grilles，but they were built more for comfort and included many of the conveniences and luxuries of the large houses which were being built in the towns.

     Unfortunately，many English castles were damaged or destroyed completely during the Civil Wars of the 1600s.

    When I spent the summer with my grandmother, she always set me down to the general store with a list. Behind the counter was a lady like no one I'd ever seen.

    “Excuse me,” I said. She looked up and said, “I'm Miss Bee.”

    “I need to get these.” I said, holding up my list. “So? Go get them. ” Miss Bee pointed to a sign. “There's no one here except you and me and I'm not your servant, so get yourself a basket from that pile.”

    I visited Miss Bee twice a week that summer. Sometimes she shortchanged me. Other times she overcharged. Going to the store was like going into battle. All summer long she found ways to trick me. No sooner had I learned how to pronounce “bicarbonate of soda” and memorized its location on the shelves than she made me hunt for it all over again. But by summer's end the shopping trip that had once taken me an hour was done in 15 minutes. The morning I was to return home, I stopped in to get some run.

    “All right, little girl,” she said. “What did you learn this summer?” “That you're a meanie!” I replied. Miss Bee just laughed and said, “I know what you think of me. Well, I don't care! My job is to teach every child I meet life lessons. When you get older you'll be glad!” Glad I met Miss Bee? Ha! The idea was absurd.

    Until one day my daughter came to me with homework troubles. “It's too hard,” she said. “Could you finish my math problems for me?”

    “If I do it for you, how will you ever learn to do it yourself?” I said. Suddenly, I was back at that general store where I had learned the hard way to add up my bill by myself. Had I ever been overcharged since?

    While WeChat is China's biggest mobile messaging app, there are many similar apps in other countries that offer similar features.

    WhatsApp (US)

    Users: more than 300 million

    Platforms: Android, iOS, Windows Phone, BlackBerry

    Features: Text chat, push-to-talk, file sharing, location sharing

    With more than 300 million active users, WhatsApp is one of WeChat's biggest competitors.

    Developed by two ex-Yahoo employees in 2009, WhatsApp originally focused on text chat, but on Aug. 6 it also started push - to - talk service. It's noted for its accessibility, ease of use and the absence of advertisements. The service is free for the first year, after which $ 0.99 (6. 06 yuan) is charged for a one –year subscription.

    Kakao Talk (South Korea)

    Users: more than 100 million

    Platform: Android, iOS, windows Phone, BlackBerry and Bada (an operate system developed by Samsung)

    Features: Text chat, group chat, push–to–talk, group calls, file sharing

    With more than 100 million users in more than 230 countries, Kakao Talk is a multi - platform (多平台) texting application that allows users to send and receive messages for tree. With Kakao Talk, users can message each other one-on-one or in group chats with unlimited numbers of friends. You can also choose from more than 250 animated emoticons and share them with friends.

    Line (Japan)

    Users: more than 200 million

    Platforms: Android, iOS, Windows Phone, BlackBerry and PC

    Features: Text chat, group chat, push–to–talk, file sharing, location sharing, gaming, stickers

    Line tops the list of the most downloaded free apps in 52 countries. Apart from text and voice messaging, Line provides its users with more than 250 original stickers and emotions to buy from its own shop. In the first quarter of 2013 alone, it made $ 17 million just from stickers. The popular app also allows friends to battle each other in the Line games.

    Very few people enjoy going to the dentist, especially for a filling. Often fillings need to be replaced during the patients' lifetime. But is filling the cavity (蛀洞)with a foreign material really the best treatment? What if the tooth could repair itself with its own material–dentine(齿质)? Researchers at King's College London have found a process that may replace the traditional method.

    Paul Sharpe of King's College says a new treatment for cavities is simpler. It uses a drug that causes the tooth to fill in the hole naturally with dentine. "It involves putting a drug in the hole. It excites a natural process, which starts to occur anyway following the damage, so you can actually get the big hole repaired and the repair is a production of the natural material, the dentine."

    Usually a new drug requires repeated testing before it is approved for treatment. However, this drug that produces the re-growth in teeth has already been approved. It is a drug used to treat Alzheimer's disease and other disorders of the nervous system. Researchers explain that they use only a small amount and they use it locally. Usually that means the medicine is put directly on the affected area. It does not travel through the patient's blood.

    Nigel Carter heads Britain's Oral Health Foundation. He describes the new treatment as an exciting possibility for dental care. But Carter also has a warning. "Actually re-growing the tooth that has been lost with a cavity would be really a huge step forward. But, it's also important that we remember that we shouldn't be getting the cavity in the first place. We're talking about a totally preventable disease."

    Here's an idea whose time has come: A flu shot that doesn't require an actual shot.

    For the first time, researchers have tested a flu vaccine patch(疫苗贴) in a human clinical trial and found that it delivered as much protection as a traditional injection(注射) with a needle. Doctors and public health experts have high hopes that it will increase the number of people who get immunized(免疫的) against the flu.

    Seasonal flu is responsible for up to half a million deaths around the world each year according to the World Health Organization. A team led by Georgia Tech engineer Mark Prausnitz has come up with an alternative method that uses "microneedles". These tiny needles are so small that 100 of them, arranged in order on a patch, can fit under your finger. Yet they're big enough to hold vaccine for three types of flu.

    None of the study volunteers had serious side effects. The groups that got patches had mild skin reactions that were not seen in the regular needle group, while the volunteers in the regular needle group were more likely to experience pain. Overall, 70 percent of the volunteers who got vaccine patches said they'd rather use them again than get a traditional flu shot. The study authors declared it a success on all fronts.

    The biggest beneficiaries could be people in low and middle-income countries, where flu vaccines are hard to come by. Reducing pain is nice, but other benefits—the patch costs less, is easier to transport, doesn't require refrigeration, can be self-administered and doesn't cause waste of needles—are even better.

    "Microneedle Patches have the potential to become ideal candidates for vaccination programs," wrote Katja Hoschler and Maria Zambon of Public Health England.

    Hi, I'm Neil Harbisso. I come from a place where the sky is always grey, where flowers are always grey, and where television is still in black and white.

    I actually come from a world where color doesn't exist. I was born with achromatopsia. I was born completely color-blind. So I've never seen color, and don't know what it looks like. But since the age of 21, I can hear color thanks to a magic electronic eye called "eyeborg": a color sensor between my eyes connected to a chip(芯片) installed at the back of my head that transforms color frequencies into sound frequencies that I hear through my bone.

    I've had the electronic eye permanently attached to my head and I've been listening to colors nonstop since 2004. So I find it completely normal now to hear colors all the time.

    Since I started to hear color, my life has changed significantly. Art galleries have become concert halls. I can hear a Picasso. And supermarkets have become like night clubs. I love how they sound.

    My sense of beauty has changed. Someone might look very beautiful but sound terrible, and someone might sound very harmonious but look awful. So I find it really exciting to create sound portraits(画像) of people. Instead of drawing the shape of someone's face I write down the different notes I hear when I look at them, and then I send them an mp3 of their face. Each face sounds different. I can even give face concerts now, concerts where I play the audience's faces. The good thing about doing this is that if the concert doesn't sound good, it's their fault.

    I also found out that things I thought were colorless are not colorless at all. Cities are not grey. Lisbon is yellow turquoise(宝石绿); London is very golden red…and humans are not black and white. Human skins range from light shades of orange to very dark shades of orange. We are all orange.

    If we extend our senses, we will consequently extend our knowledge.