The streams are about 12 to 15 feet wide and 300 feet or more long, scientists said. "What we're dealing with is wet soil, thin layers of wet soil, not standing water," said Aifred  McEwen of the University of Arizona at Tueson! the principal scientist for the Mars Reconnaissance Orbiter's high-resolution imaging experiment,

     Because liquid water is essential to life, the findings could have major implications for the possibility of Martianlife, There searchers said further exploration is needed to determine whether microscopic life exists on the planet.

    The presence of liquid water could also make life easier for astronauts visiting or living on Mars. Watercould be used for drinking and for creating oxygen and rocket fuel. NASA's goal is to send humans there inthe 2030s.

    The evidence of flowing water consistslargely of dark, narrow streaks(条痕) on the surface that tend to appear and growd uring the warmest Martian months and fade the rest of the year.

    Mars is extremely cold even in summer,and the streaks are in places where the temperature is as low as minus 10 degrees Fahrenheit. But salt can lower the freezing point of water and melt ice.

    The source of the water is a mystery. Scientists noted it could be melting ice. It could be an underground a quifer, which is rock or sand that can hold water. It is possibly water vapor from the thin Martian atmosphere, Or it may be a combination Michael Meyer, lead scientistfor NASA's Mars exploration program, said the only definitive way for now to determine whether there's life on Mars is to collect rocks and soil foranalysis on Earth - something a U.S. lander set for lift-off in 2020 will do.

    A child who has once been pleased with a tale likes, as a rule, to have it retold in almost the same words, but this should not lead parents to treat printed fairy stories as formal texts. It is always much better to tell a story than read it out of a book, and, if a parent can produce what, in the actual situation of the time and the child, is an improvement on the printed text, so much the better.

    A charge made against fairy tales is that they harm the child by frightening him or making him sad thinking. To prove the latter, one would have to show in a controlled experiment that children who have read fairy stories were more often sorry for cruelty than those who had not. As to fears, there are, I think, some cases of children being dangerously terrified by some fairy story. Often, however, this arises from the child having heard the story once. Familiarity with the story by repetition turns the pain of fear into the pleasure of a fear faced and mastered.

    There are also people who object to fairy stories on the grounds that they are not objectively true, that giants, witches, two - headed dragons, magic carpets, etc. do not exist; and that, instead of being fond of the strange side in fairy tales, the child should be taught to learn the reality by studying history. I find such people, I must say so peculiar (奇怪的, 异常的) that I do not know how to argue with them. If their cases were sound, the world should be full of mad men attempting to fly from New York to Philadelphia on a stick or covering a telephone with kisses in the belief that it was their beloved girl -friend.

    No fairy story ever declared to be a description of the real world and no clever child has ever believed that it was.

    In American schools there is something called Homecoming Day. Many high schools and colleges with a football team have a homecoming game. This can be the most important event of the year except graduation or commencement day(毕业典礼)．Students plan Homecoming Day for many weeks in advance.

    Several days before Homecoming，students start to decorate the school. There are signs to wish luck to the team，and many other signs to welcome all the graduates. Many people still come to Homecoming twenty or thirty years after their graduation.

    The members of school clubs build booths(摊位) and sell lemonade(柠檬)，apples and sandwiches. Some clubs help to welcome visitors.

    During the day people like to look for teachers that they remember from long ago. Often they see old friends and they talk together about those happy years in school.

    Everyone soon comes to watch the football game. When the game is half over，the band comes onto the field and plays school songs. Another important moment is when the Homecoming Queen or King appears. All the students vote a most popular student. It is a great honor to be chosen.

    Homecoming is a happy day，but it is not perfect unless the football team wins the game. Even if the team loses，the students still enjoy Homecoming. Some stay at the school to dance，and others go to a party. For everyone it is a day worth remembering.

    The British are known for their sense of humor. However, it is often difficult for foreigners to understand their jokes. The main point to remember is that the British often use understatement.

     Understatement means saying less than you think or feel. For example, if someone gets very wet in a shower of rain, he might say, “It's a little damp (潮湿的) outside.” Or, if someone is very impolite and shouts at another person, someone else might say, “She isn't exactly friendly.” Understatement is often used in unpleasant situation or to make another person look silly. Understatement plays an important part in British humor.

    Another key to understanding British humor is that the British like to make fun of themselves as well as others. They often laugh about the silly and unpleasant things that happen to our everyday life when someone accidently falls over in the street. They also like to make jokes about people from different classes of society. They like to make jokes about their accents, the way they dress and the way they behave. What's more, the British love to watch comedies (喜剧) about people who do not know how to behave in society. The comedies series Mr. Bean is a good example of this kind of humor.

    Mr. Bean is the character created by British actor Rowan Atkinson in 1990. Mr. Bean doesn't talk often, and instead he uses his body movement and facial expressions to make people laugh. Perhaps what makes Mr. Bean so funny is that he does things that adults in the real world cannot do. Mr. Bean is popular in many countries around the world because you do not have to speak English to understand the humor. Because of this, many people have become familiar with the British sense of humor.

    If you are in Dubai you may notice a robot police officer sharing the street with you. Your first thought might be, “Have I walked into a movie set？”

    The answer is no. That robot is Dubai's newest police officer. The robot has a touch screen instead of a gun. The robot will be employed mostly at shopping centers and other places popular with visitors.

    The robot's face has eyes but no mouth or nose. It stands 165 centimeters tall and weighs 100 kilograms. If the robot works well, Dubai says 25 percent of its police force could be robots by 2030. The robot cop(巡警) was officially presented at Dubai's Gulf Information and Security Expo and Conference in May.

    The police hope the robot will make life easier for the people of Dubai. Khalid Al Razooqi is Director General of Smart Services at the Dubai Police. He said the robot can help the public every day, and that “it won't ask for any sick leave”.

    The robot cannot make arrests (逮捕). But it can recognize faces and compare them to photographs on a criminal database. It can also sense emotions. People can use the robot's touch screen to do things like reporting a crime, paying fines and reporting lost or found things. They can also ask how to get somewhere. The robot can greet and shake hands with people. So far, the robot can speak Arabic and English. It soon will learn other languages such as Russian, Chinese, French and Spanish. In addition to having a touch screen, the robot has a camera that can live stream video to a police command center.

    Dubai has plans to add other kinds of robots to its police force. Within two years, the city plans to use a three meter tall robot that can run up to 80 kilometers an hour. The Dubai government says the machine would be the world's largest robot. A human police officer will be able to sit inside and control the robot. It will be able to lift heavy objects.

    The city also plans to use an egg shaped robot to control parking areas and give tickets to people who break traffic laws.

After years of travel it was bound to happen. Waiting by the moving belt, I watched the suitcases make mocking(嘲弄的) rounds. My companions, exhausted after16hours in the plane, were sympathetic and relieved. They were all thinking: at least it wasn't me. Any moment now, I told myself, swearing at the happy vacationers busy collecting their things. What about my necessities (必需品)?

For millions of travelers a year, it happens. Their missing bags stolen, sold in blind auctions(拍卖), or gone forever without any explanation. Today it was my turn, in a crowded Indian airport, as far from home as I'd ever been.

So, while the airline hunted for my belongings with no any order or plan and asked whether I would rather have $200– I found myself wandering the hot streets of Delhi in an orange dress and a pair of blister-producing ballet flats. Equipped with my carry-on (contents: eyeglasses, a paperback, an ancient tube of Chapstick), I was forced to "manage".

Day two, good news. The bag had been found! Bad news: it is still sitting in Toronto. Did it miss me as much as I missed it?

But then, a twist. I survived. By day three, I was secretly enjoying myself. What to wear? Hello, orange. Make-up today? Not an option. With almost nothing, I found better things: a new understanding of necessity, a short break from my obsession(痴迷) with stuff, stuff and more stuff, and a new appreciation for what does matter (the Taj Mahal) , when my bag finally made its way back to me.

That's right, my jam-packed blue suitcase resurfaced – on day four – and I suddenly had a rainbow of ten dresses to choose from. I decided to wear my orange dress once more, for good luck. It worked: nothing went missing on my journey home.