Exercise may help to safeguard the mind against depression through previously unknown effects on working muscles, according to a new study involving mice.

    Mental health experts have long been aware that even mild, repeated stress can contribute to the development of depression and other mood disorders in animals and people. Scientists have also known that exercise seems to cushion against depression. But precisely how exercise, a physical activity can lessen someone's risk for depression, a mood state, has been mysterious. So for the new study, researchers at the Karolinska Institute in Stockholm studied the brains and behavior of mice in a complicated and novel fashion.

    We can't ask mice if they are feeling cheerful or in low spirits. Instead, researchers have pictured certain behaviors that indicate depression in mice. If animals lose weight, stop seeking out a sugar solution when it's available — because, probably, they no longer experience normal pleasures — or give up trying to escape from the cold-water zone just freeze in place, they are categorized as depressed. And in the new experiment, after five weeks of frequent but low-level stress, such as being lightly shocked, mice displayed exactly those behaviors. They became depressed.

    The scientists could then have tested whether exercise blunts (延缓) the risk of developing depression after stress by having mice run first. But, frankly, from earlier research, they wanted to know how, so they bred pre-exercised mice. A wealth of earlier research by these scientists and others had shown that aerobic exercise, in both mice and people, increases the production within muscles of an enzyme (酶) called PGC-1alpha. The Karolinska scientists suspected that this enzyme somehow creates conditions within the body that protect the brain against depression. Then, the scientists exposed the animals, which without exercising, were in high levels of PGC-1alpha to five weeks of mild stress. The mice responded with slight symptoms of worry. But they did not develop depression. They continued to seek out sugar and fought to get out of the cold-water zone. Their high levels of PGC-1alpha appeared to make them depression-resistant. Finally, to ensure that these findings are relevant to people, the researchers had a group of adult volunteers complete three weeks of frequent endurance training, consisting of 40 to 50 minutes of moderate cycling or jogging. The scientists conducted muscle biopsies (活体检查) before and after the program and found that by the end of the three weeks, the volunteers' muscle cells contained substantially more PGC-1alpha than at the study's start. The finding of these results, in the simplest terms, is that “you reduce the risk of getting depression when you exercise,” said Maria Lindskog, a researcher at the Karolinska Institute.

    Welcome to your future life!

    You get up in the morning and look into the mirror. Your face is firm and young-looking. In 2035, medical technology is better than ever. Many people your age could live to be 150, so at 40, you're not old at all. And your parents just had an anti-aging(抗衰老的) treatment. Now, all three of you look the same age !

    You say to your shirt, “Turn red.” It changes from blue to red. In 2035, “smart clothes” contain particles(粒子) much smaller than the cells in your body. The particles can be programmed to change your clothes' color or pattern.

    You walk into the kitchen. You pick up the milk, but a voice says, “You shouldn't drink that!” Your fridge has read the chip (芯片) that contains information about the milk , and it knows the milk is old . In 2035, every article of food in the grocery store has such a chip.

    It's time to go to work. In 2035, cars drive themselves. Just tell your “smart car” where to go. On the way, you can call a friend using your jacket sleeve(袖子). Such “smart technology” is all around you.

    So will all these things come true? “For new technology to succeed,” says scientist Andrew Zolli , “it has to be so much better that it replaces what we have already.” The Internet is one example --what will be the next?

根据短文内容，选择最佳答案，并将选定答案的字母标号填在题前括号内。

    Author Norman Mailer published an essay in which he declared the graffiti(涂鸦) of the New York subway to be "The Great Art of the 70s". But what happened to the artists and why is there no subway graffiti any more?

    "It started with someone just writing their name — someone saw that, and added on to it," recalls New York graffiti artist Nicer, born Hector Nazario. "Letters going in front of letters, coming back through a letter, behind a letter, going across a letter... the subways became our playground," adds Riff170.

    New York in 1974 was a city in crisis. The Mayor, Abe Beame, slashed the city's budget in a bid to stave off bankruptcy(破产), which meant laying off school teachers, police officers and subway staff.

    "They were taking the money from the schools, there was a lot of corruption here, in this community, and so they took the after-school programmes away, and there was no outlets for this. So the outlet became our city," says Bronx-born designer Eric Orr.

    "It was like an explosion. The graffiti explosion. All of a sudden it took over the whole city. I don't know what happened, but overnight in the early 70s it was from no graffiti to all graffiti," says another former artist, Flint Gennari.

    Eric Felisbret, author and former graffiti artist, says graffiti culture was in a way a product of the civil rights movement. "It was never political," he says, "but many people were brought up with that, and to express yourself by breaking the law became a natural process for them."

    The graffiti pioneers came from all races, however. "There were writers that were African American, Latino - Puerto Rico, Dominican, Cuban - Jewish, Asian, and it became one unit — one family," says another graffiti pioneer, Roberto Gualtieri.

    Prof Gregory Snyder, sociologist and author of Graffiti Lives, says: "For lots of people, graffiti is ugly, vandalistic, and I'm not denying that. It's vandalism... now, oftentimes it's very clever vandalism. It can be written on a dumpster, like a garbage bin, and if someone's attempting to make a garbage bin look a little prettier maybe that's not the worst thing in the world." Although Mailer was not alone in welcoming the flowering of creativity, the authorities hated it, as did many passengers.

    So when Mayor Ed Koch took office, he was determined to clean up the city and set about targeting graffiti.

    "I remember in 1982 he brought everyone out to a train yard and there was a single train painted white," says former New York Daily News reporter Salvatore Arena. Trains were taken out of service and cleaned as soon as graffiti was spotted. Carriages were protected at night and the city agreed to ban the sale of spray cans.

    If in 1984 80% of subway carriages contained graffiti by May 1989 the network was graffiti-free. “Graffiti has gone through an evolution, and it will continue to evolve. It's now socially accepted in places where 20-30 years ago that would have been impossible. It's now showcased(展示) in certain museums —and let's say in another 30 years from now it may be hanging in the White House,” says Nicer.

    Nowadays painted graffiti is largely gone from the New York subway trains themselves and is seen instead on the walls and tunnels of the city. It has been replaced by scratchiti(刮擦艺术) created onto carriage windows using keys, knives. Unlike the vivid images of 40 years ago, these ghostly patterns are somehow easy to ignore. After all, graffiti has faded quietly into the background.

    When my brother and I were young, my mom would take us on Transportation Days.

    It goes like this: You can't take any means of transportation more than once. We would start from home, walking two blocks to the rail station. We'd take the train into the city center, then a bus, switching to the tram, then maybe a taxi. We always considered taking a horse carriage in the historic district, but we didn't like the way the horses were treated, so we never did. At the end of the day, we took the subway to our closest station, where Mom's friend was waiting to give us a ride home—our first car ride of the day.

    The good thing about Transportation Days is not only that Mom taught us how to get around. She was born to be multimodal (多方式的). She understood that depending on cars only was a failure of imagination and, above all, a failure of confidence—the product of a childhood not spent exploring subway tunnels.

    Once you learn the route map and step with certainty over the gap between the train and the platform, nothing is frightening anymore. New cities are just light-rail lines to be explored. And your personal car, if you have one, becomes just one more tool in the toolbox—and often an inadequate one, limiting both your mobility and your wallet.

    On Transportation Days, we might stop for lunch on Chestnut Street or buy a new book or toy, but the transportation was the point. First, it was exciting enough to watch the world speed by from the train window. As I got older, my mom helped me unlock the mysteries that would otherwise have paralyzed my first attempts to do it myself: How do I know where to get off? How do I know how much it costs? How do I know when I need tickets, and where to get them? What track, what line, which direction, where's the stop, and will I get wet when we go under the river?

    I'm writing this right now on an airplane, a means we didn't try on our Transportation Days and, we now know, the dirtiest and most polluting of them all. My flight routed me through Philadelphia. My multimodal mom met me for dinner in the airport. She took a train to meet me.

Dogs are man's best friends—they are very good for children's health. Researchers found that family pets helped to protect babies against breathing problems and infections (感染).

    A team from Kuopio University Hospital in Finland studied 397 babies born at their hospital between September 2012 and May 2015 for their first year. They found that babies who lived with a dog or a cat spent fewer weeks with ear infections, coughs or runny noses. They were also less likely to need antibiotics (抗生素) than babies in homes without a pet.

    Study author, Dr. Eija Bergroth, said dogs brought dirt and bacteria (细菌) into the home, which helped children's immune system (免疫系统) to be strong. This improved their defenses against bacteria.

    As part of the study, parents filled out weekly diaries starting when the children were nine weeks old, recording information on babies' health as well as their contact with cats and dogs. They recorded if they had fever, ear infections, coughs or running noses. They also put down whether they needed antibiotics.

    Based on those diaries, the researchers found that about a third of the children spent most of their first year with a pet dog and 24 percent in a home with a cat. And children with no dog contact at home were healthy for 65 percent of the time, compared to between 72 and 76 percent for those who did have a pet.

    The researchers also found that contact with dogs, more than cats, was tied to fewer weeks of sickness for babies.

    However, the researchers said they couldn't rule out the possibility that people who own dogs are less likely to get sick for another reason, not due to any protection offered by pets.

Guide to Stockholm University Library

    Our library offers different types of studying places and provides a good studying environment.

Zones

    The library is divided into different zones. The upper floor is a quiet zone with over a thousand places for silent reading, and places where you can sit and work with your own computer. The reading places consist mostly of tables and chairs. The ground floor is the zone where you can talk. Here you can find sofas and armchairs for group work.

Computers

    You can use your own computer to connect to the wi-fi specially prepared for notebook computers; you can also use library computers, which contain the most commonly used applications, such as Microsoft Office. They are situated in the area known as the Experimental Field on the ground floor.

Group-study places

    If you want to discuss freely without disturbing others, you can book a study room or sit at a table on the ground floor. Some study rooms are for 2～3 people and others can hold up to 6～8 people. All rooms are marked on the library maps.

    There are 40 group-study rooms that must be booked via the website. To book, you need an active University account and a valid University card. You can use a room three hours per day, nine hours at most per week.

    Storage of Study Material

    The library has lockers for students to store course literature. When you have obtained at least 40 credits, you may rent a locker and pay 400 SEK for a year's rental period.

    Rules to be Followed

    Mobile phone conversations are not permitted anywhere in the library. Keep your phone on silent as if you were in a lecture and exit the library if you need to receive calls.

    Please note that food and fruit are forbidden in the library, but you are allowed to have drinks and sweets with you.