Paris

Passengers carried per day: 4.4m

Cost of ticket: 80p flat fare

Length: 131 miles    Lines: 14   Stations: 297

    In Paris there are pleasures for those who use the Metro(地铁) — many of them artistic. The graceful Art Nouveau dragon-fly entrances are just the most noticeable on a Metro system which celebrated its 100^th anniversary by spending 30 million francs (£2.9million) on making its stations works of art. On my way home I pass Bonne Nouvelle station in the heart of Paris's cinema district. There, during the cinema festival this summer, special lighting effects dot the platforms and films are projected onto the large advertising boards.

    More than anything the metro is efficient. “When I worked on line 4”, says a retired driver, “we had exactly 30 minutes and 15 seconds to complete the journey. If it took any longer, they cut our pay.” But there are problems. Many Metro stations have too many stairs, and changing lines at big interchanges(交换) can be tiresome.

Moscow

Passengers carried per day: 9m

Cost of ticket: 12p

Length: 164 miles    Lines: 11   Stations: 162

    The first underground passage for the Moscow Metropolitan started in 1932. Three years later the trains started running. They haven't stopped since— every 90 seconds or two minutes during rush hour, every five minutes the rest of the time, from 6 a.m. till 1 a. m. There may be a crowd of people but there is seldom a wait.

    The trains take you through spacious and spotless stations. For tourists it's a major sightseeing attraction: from Russian Art Deco to neo-classical, the Metro stations are not to be missed.

Tokyo

Passengers carried per day: 7m

Cost of ticket: 90p ~ £1.68

Length: 177 miles    Lines: 12   Stations: 209

    Trains do not just arrive on time in Tokyo. They stop right on the platform mark so that passengers can line up knowing exactly where the doors will open. Train driving is a respectful job for life, for which the applicants must pass a strict screening of health checks, interviews and written exams before they can put on the enviable uniform, cap and white gloves.

    However, overcrowding means it is far from perfect. At rush hours, some stations employ part-time platform staff to push in passengers. Carriages can be filled to 184% of capacity(容量). The main reason for such conditions is that the Tokyo subway station system has only 15 miles of track for every 1 million people, compared to 36 on the London Underground. New lines are under construction, but at a cost of £500,000 per meter of rail. Progress has been slow.

Mexico City

Passengers carried per day: 4.2m

Cost of ticket: 11p flat fare

Length: 99 miles    Lines: 11   Stations: 175

    Fast, relatively safe, and very cheap, Mexico City's underground is an ideal place of order and efficiency compared to the disorders above. The Mexican capital's underground system is the biggest in the continent and one of the most subsidized (获得补助的) networks in the world.

    The first trains leave the station at 5 a.m. and the last after midnight as the crowd move from the outskirts of the 20 million-strong megacity (大城市). Mexico City's Metro also attracts a sizeable group of passengers who are unwilling to spend hours in traffic jams. There is a master plan to build new lines and extend existing one, but financial constraints (约束) complicated by the fact that the system runs through different jurisdicitons (管辖权) mean progress is slow.

    In cooperation with German experts, several scientists from the University of Bradford believe that they finally solved a mystery that has been confusing millions of people: why our hair turns gray with age.

    The researchers came up with their results by examining native hair and cells from human hair follicles（毛囊）. They say the secret turns out to be hidden in catalase（过氧化氢酶）, which is causing hair to turn gray.

    Catalase production goes down with age and stress, allowing hydrogen peroxide（过氧化氢） in the hair to do its favorite job—making hair gray, and then white, by blocking the normal production of melanin（黑色素）. Melanin is our hair's natural pigment that is responsible for the color of hair. It also determines the color of our eyes and skin.

    Dr. Gerald Weizmann, an editor of a journal, says," All of our hair cells make a tiny bit of hydrogen peroxide, but as we get older, this little bit becomes quite a lot, and our hair turns gray and then white."

    The new study brings hope for millions of people who have to color their hair: to finally obtain some shampoo that will decrease levels of hydrogen peroxide and therefore restore gray or white hair to its natural color or even prevent it from turning gray.

    The researchers are already conducting an experiment with such a drug on a few volunteers with gray hair and expect to get the results in the next two to three months. If everything works out, millions of people will choose between this drug and other previously used expensive dyes. However, even if the drug works, it will take at least several years before it can be brought to the market.

    For high school leavers starting out in the working world, it is very important to learn particular skills and practice how to behave in an interview or how to find an internship (实习). In some countries, schools have programs to help students onto the path to work. In the United States, however, such programs are still few and far between.

    Research shows that if high schools provide career-relat­ed courses, students are likely to get higher earnings in later years. The students are more likely to stay in school, graduate and go on to higher education.

    In Germany, students as young as 13 and 14 are expected to do internships. German companies work with schools to make sure that young people get the education they need for future employment.

    But in America, education reform programs focus on how well students do in exams instead of bringing them into contact with the working world. Harvard Education school professor Robert Schwartz has criticized education reformers for trying to place all graduates directly on the four-year college track. Schwartz argued that this approach leaves the country's most vulnerable (易受影响的)kids with no jobs and no skills.

    Schwartz believed that the best career programs encour­age kids to go for higher education while also teaching them valuable practical skills at high school. James Madison High School in New York, for example, encourages students to choose classes on career-based courses. The school then helps them gain on-the-job experience in those fields while they're still at high school.

    However, even for teens whose schools encourage them to connect with work, the job market is daunting. In the US，unemployment rates for 16-to 19-year-olds are above 20 percent for the third summer in a row.

"The risk is that if teenagers miss out on the summer job experience, they become part of this generation of teens who had trouble in landing a job," said Michael, a researcher in the US.

    Astronomers have taken the first ever image of a black hole, which is located in a distant galaxy (星系).The black hole is 500 million trillion km away and was photographed by a network of eight telescopes across the world. It was captured by the Event Horizon Telescope (EHT).

    The announcement was made in Washington, Brussels, Santiago, Shanghai, Taipei and Tokyo. Details have been published today in Astrophysical Journal Letters.

    Prof Heino Falckc, of Radboud University in the Netherlands, who suggested the experiment, told BBC News that the black hole was found in a galaxy called M87. "What we see is larger than the size of our entire Solar System," he said. "It has a mass 6.5 billion times that of the Sun. And it is one of the heaviest black holes that we think exists. It is an absolute monster, the heavyweight champion of black holes in the Universe."

    The image shows an intensely bright "ring of fire", as Prof Falckc describes it, surrounding a perfectly circular dark hole. The bright halo is caused by very heated gas falling into the hole. The light is brighter than all the billions of other stars in the galaxy combined - which is why it can be seen at such distance from Earth. The edge of the dark circle at the center is the point at which the gas enters the black hole, which is an object that has such a large gravitational pull (万有引 力）,not even light can escape.

    "It is remarkable that the image we observe is so similar to that which we get from our theoretical calculations. So far, it looks like Einstein is correct once again." said Dr Ziri Younsi, of University College London -who is part of the EHT cooperation.

    Chinese scientists were involved in the observation through a telescope in Hawaii. They were also highly involved in follow-up data processing and theoretical analysis, said Shen Zhiqiang, head of the Chinese Academy of Sciences' Shanhai Astronomical Observatory and a member of the EHT international team.

    Shanghai and Taipei were selected as two of the cities to hold news conferences, together with Washington, Brussels, Santiago and Tokyo, a recognition of China's contribution.

    "In the fields of astronomy, radio astronomy, and space astrophysics, China has made a significant contribution to this global project," Falcke said.

    Do you often feel like you want to wash your hands again and again? Or do you ever have the urge to line up the items on your desk? These all may be symptoms of obsessive-compulsive disorder (强迫症), or OCD, which affects about 2 percent of the world's population.

    Those who suffer from OCD have difficulty finding successful treatment because doctors don't clearly understand its causes. But now, a new study has given hope for a future cure.

    For the study, which was published in the journal Nature in October, researchers observed humans, dogs and mice. They discovered four genes that may be responsible for obsessive-compulsive behaviors in humans.

    But why observe dogs and mice to learn about humans?

    "Dogs, it turns out, are surprisingly similar to people," study author and geneticist Elinor Karlsson, of the Broad Institute of MIT and Harvard University, US, told NPR. "They're chasing their own tail or chasing shadows like normal, but they're doing it for hours."

    In the study, researchers made a list of about 600 genes in mice, dogs and humans that they thought might cause OCD, reported NPR. They then compared those genes in two large groups of people – those who don't have OCD and those who do. In the end, they identified just four genes with mutations (突变) in the OCD group. The genes are active in a neurological pathway (神经通路) in the brain, which is believed to help control actions. But the mutations could block the neurological pathway.

    For example, for people without OCD, when they finish washing their hands, a signal will come, telling them to stop. But for people with OCD, the neurological pathway is blocked, so the message isn't getting through. As a result, the person will continue to wash their hands.

    "OCD and anxiety are kind of like learning disorders," Marcos Grados, an OCD researcher at Johns Hopkins University School of Medicine, told NPR. "Often with OCD, people have a fear of germs (细菌). You can't touch tables or door knobs (把手) and every time it's the same sensation (感觉). You didn't learn that the last time you touched a door knob, nothing happened. It's like touching it for the first time ever."

    However, that doesn't mean people who have these genetic mutations will always have obsessive-compulsive behaviors, the researchers said. That's because the disorder also relies on other things, such as one's environment.

    According to reports, various existing treatment methods have low success rates in patients. But now that we know where OCD comes from, let's hope we will soon find an effective way to treat it.

As I prepared for my Level 8 Royal Conservatory of Music piano exam, memories of previous disappointing marks filled me with dread and anxiety. The mere thought of booking the exam made me feel completely strained. However, fate had other plans in store for me.

Just when I thought things couldn't get any worse, my trusty 10﹣year﹣old electric piano malfunctioned. The middle C note played as an F﹣sharp, and multiple other keys were out of tune.

Despite my distress, my father refused to buy a new piano and instead urged me to be more resourceful. Initially, I was at a loss without my beloved electric piano. But after struggling for a few days, I was determined to find every available piano room on campus. After discovering hidden pianos in corners, I spent countless hours practicing. As my exam drew near

One day, while practicing in a piano room, one of my teachers walked in and offered me a mini exam. To my surprise, I found a place where I could be anyone.

Playing the piano became my escape from the anxieties of adolescence and allowed me to express myself freely. When it was time to play in front of the examiner, I no longer feared judgment. Instead, I only feared not being able to represent all my hard work. As the lights came on

Eventually, I received my mark. Not only did I achieve a rarely given "well done", but I also discovered a newfound appreciation for music. Whenever I feel discouraged, some lessons are best learned the hard way.