If you see a group of people dancing and singing on the street or in the railway station,  you don't need to feel surprised．They are a flash mob （快闪族）, which is a group of people who come together suddenly in a public place, do something unusual for a brief period of time,  and then quickly break up．They are usually organized with the help of the Internet or other digital communication network．At a predetermined time, they gather and perform some  distractions（消遣） such as waving their hands and exchanging books, Then, they quickly break up before the police can arrive．Using mobile phones, the flash mob can change its location if the first one has been replaced for any reason．

    Bill Lasik, senior editor of Harper's Magazine, organized the first flash mob in Manhattan in May 2003 and the first successful flash mob came together on June 3, 2003 - after the first try was foiled at Macy's department store．Lasik claimed that the activity was designed to make fun of hipsters （起时髦的人）, and call attention to the cultural atmosphere．

    Flash mob gatherings can sometimes shock people．Such an activity might seem amusing and untrue, but it also might frighten people who are not aware of what is taking place．Undoubtedly, flash mobs can serve as good political tools in any direction．They also have great economic potential, such as using flash mobs to advertise a product．

    The flash mob is now becoming more and more popular．People use it to do many things．For example, in 2009, Michael Jackson's fans took part in a flash mob to remember him．Hundreds of his fans gathered singing and dancing Michael's famous song "Beat It" together．Flash mobs give people from all walks of life an opportunity to come together to create a memory．

    Should we allow modern buildings to be built next to older buildings in a historic area of a city? In order to answer this question, we must first examine whether people really want to preserve the historic feel of an area. Not all historical buildings are attractive. However, there may be other reasons—for example, economic (经济的) reasons—why they should be preserved. So, let us assume that historical buildings are both attractive and important to the majority of people. What should we do then if a new building is needed?

    In my view, new architectural styles can exist perfectly well alongside an older style. Indeed, there are many examples in my own home town of Tours where modern designs have been placed very successfully next to old buildings. As long as the building in question is pleasing and does not dominate (影响) its surroundings too much, it often improves the attractiveness of the area.

    It is true that there are examples of new buildings which have spoilt (破坏) the area they are in, but the same can be said of some old buildings too. Yet people still speak against new buildings in historic areas. I think this is simply because people are naturally conservative(保守的)and do not like change.

    Although we have to respect people's feelings as fellow users of the buildings, I believe that it is the duty of the architect and planner to move things forward. If we always reproduced what was there before, we would all still be living in caves. Thus, I would argue against copying previous architectural styles and choose something fresh and different, even though that might be the more risky choice.

    In America, parents tend to encourage their children to develop their potential (潜能) to the fullest extent. Fathers and mothers frequently teach their children both ambition and the confidence necessary to work toward their goals. American parents are always active in concentrating on what their kids can do, not what they can't. As a result, millions of American boys and girls grow up hoping to become actors and athletes, diplomats and doctors. Many of them even want to become president.

    American parents often encourage their children to become involved in extra activities of all types at school, such as student government, sports and music. They believe that only through taking part in these activities can their children become mature young adults.

As we all know, school work is important. But parents should realize that the social skills their children learn from natural conversations with each other are as important as schoolwork and the skills they will need in the future work. What's more important in their work is that their children should have a sound knowledge of physics or the ability to communicate effectively.

As a rule, Chinese parents don't educate their children about the same kind of ambition and confidence as Americans do, nor do they encourage the same level of participation in extra activities. Children are typically advised to study hard and pass exams. They have to spend a lot of time in doing much schoolwork every day. It is a great waste of time to do so.

Now more and more Chinese parents have recognized that they should pay attention to developing the potential of their children. I hope that leaders in Chinese educational circles should take some measures to develop the potential of their children. I am very confident about it.

    The American Heart Association (AHA) says that too many people are spending far too much time on chairs and couches. "Based on existing evidence, we found that U.S. adults are sedentary for about six to eight hours a day, "said Deborah Rohm Young, chair of AHA panel that wrote the new advisory.

    According to the AHA, growing evidence shows that, on its own, exercise isn't enough to cancel out the unhealthy effects of sitting for a long time. "Regardless of how much physical activity someone gets, long sedentary time could negatively influence the health of your heart and blood vessels," Young explained.

    The exact mechanisms behind the effect aren't yet clear. “There are many important factors we don't understand about sedentary time yet," Young said. She stressed that, "the types of studies available identify trends but don't prove cause and effect.”

    "We don't have information about how much sedentary behavior is bad for health — the best advice at this time is to 'sit less and move more,” she added.

    How much more? According to the AHA, people should try to get at least 30 minutes of moderate to vigorous (剧烈的）exercise a day to reach the recommended 150 minutes of moderate exercise or 75 minutes of vigorous exercise a week, That's healthier than trying to cram their weekly exercise into one or two days, according to the statement.

    "The real risk simply comes down to the amount we sit, without there being a true medicine or method to control the harmful effects," said Steinbaum, a preventive specialist in heart disease.

    Still, society has evolved to encourage sitting, she added.

    "Our lives have become focused around activities requiring us to be still—whether it be transportation, our computers, or the television or computer in our leisure time,” Steinbaum said. "Sociologically, instead of being active to be productive or to have enjoyment, our productivity and fun often requires minimal physical activities."

    Most dog owners are convinced that their four-legged friends know exactly what they mean when they use certain words like sit, stay or treat. However, researchers have always wondered whether dogs really understand human speech or if they rely on other information to get the meaning. For example, does the word “fetch” form a picture of a stick or ball in the dog's mind, or does the dog bring back the object based on the owner's voice or gesture? A new study by scientists at Atlanta's Emory University seems to indicate that “man's best friend” does indeed know what the owner is saying.

    The researchers began by asking the owners of twelve dogs of various kinds to train their pets to identify two toys of different materials, such as a toy animal and a ball. Once the dogs had mastered the task, they took turns inside a special scanner. The owners then tested their dog's language skill by first calling out the names of the toys they had been trained to recognize and then saying meaningless words such as “bobbu” and “bodmick” while holding up random objects the dogs hadn't seen before.

    The scans suggested that the parts of the dogs' brains responsible for processing of sounds showed different brain patterns when they heard words they were familiar with, compared with the ones they had never heard before. While that was not enough to prove that the dogs were picturing their toys when they heard the word, it did indicate some sort of recognition. The researchers believe this is an important step forward in understanding how dogs process language.

    Even more interesting was that the dog's brains showed a higher level of neural(神经)activity at the sound of unknown words. This is the exact opposite of what happens in human brains, which get more active at the sound of familiar words. The researchers say the dogs may become cheerful at the sound of new words to try to understand them in the hope of delighting their masters. “Dogs want to please their owners, and perhaps also receive praise or food,” says Empty neuroscientist Gregory Burns, senior author of the study.

    However, though your pet may understand human speech, the scientists recommend using visual signals and smell for training. “When people want to teach their dog a trick, they often use spoken command because that's what humans prefer, ”Prichard says.“ From the dog's view, however, a visual command might be more effective, helping the dog learn the trick faster.”

On the day the tornado hit, there was no indication severe weather was on its way—the sky was blue and the sun had been out. The first alert my husband, Jimmy, 67, and I, 65, got came around 9 p. m. , from some scrolling text on the TV Jimmy was watching. He ran upstairs to find me in our third-floor bedroom, and we changed the channel from the presidential primary debate I had been watching to our local Pensacola, Florida, station.

No sooner had we found coverage of the tornado than it was on top of us. It was the loudest thing I have ever heard. The bones of the house shook, and the power went out. Pink insulation flew into the room from a trapdoor to the attic, and the wind began to roar through the house.

I didn't know how or if we would make it down the steps. It felt as if there were no floor underneath me as the wind lifted me off my feet. I gripped the banister (栏杆) and tried to move forward, but this intense pressure held me in place.

By the time I reached the closet, the tornado had been over us for about a minute. Jimmy pushed me down to the closet floor, but he couldn't get inside himself because of the wind. I gripped Jimmy's arm. My knees and scalp were full of glass, but in that moment, I felt no pain.

All of a sudden, Jimmy lifted off his feet like people in tornadoes do in the movies. I thought he was gone. And then everything stopped. He landed on his feet. In those first quiet moments, I couldn't believe it was over. Jimmy said he'd go outside to check. "No," I said. "Don't leave me. "

Our neighbor says the storm lasted four minutes. In that time, four of the twelve town houses in our unit were completely destroyed. Of the houses left standing, ours suffered the most damage. Amazingly, none of us were severely injured.