There are some injuries that are common to all types of extreme sports. The following are some of the important things to do to prevent extreme sports injuries. {#blank#}1{#/blank#} But they can definitely minimize the risk of injuries.

    Warm up.

    {#blank#}2{#/blank#} They include a combination of cardiovascular(心脏血管的)exercises, strength drills and stretching. Cardiovascular exercises increase body temperature, heart rate and blood circulation, which is required for further movement of the body. Strength drills increase the stamina of the body, while stretching warms up the muscles preparing them for sudden forceful movements. {#blank#}3{#/blank#} It also plays an important role in boosting the team spirit for a team sport. A warm-up session should last for at least 20 minutes and it can extend up to half an hour.

    Avoid overworking.

    There are some people who do not exercise their body for the sport on a regular basis and perform a week's task in a day or two. {#blank#}4{#/blank#} They do not realize the effect of overworking during the performance and keep doing it until they feel extremely tired. Apart from the actual sport, one should also avoid overdoing the warm-up exercises before the activity.

    {#blank#}5{#/blank#}

    Just as warming up is essential before any rigorous(充满活力的) physical activity, cooling down the body after playing a rigorous sport is also a significant part of physical conditioning. When you are done with your sports session, you can conclude with some walking, jogging or light running. Slight stretching exercises, focusing on specific muscles, will also be useful for cooling down the body.

A. Cool yourself down.

B. Look for a coach to train you.

C. These people are likely to suffer from extreme sport injuries.

D. However, there are no perfect methods which can assure you 100% safety.

E. Along with physical preparation, warming up prepares you mentally to begin a sport.

F. You should also be careful about your clothing selection for warmth and protection.

G. Warm-up exercises are very important before you begin any sports practice.

    One of the traditions which is now a necessary part of Christmas is that of Father Christmas, or Santa Claus. According to the modern legend, he is a magical figure who visits all the children of the world during the night before Christmas Day, leaving presents, which they find the next morning. He flies through the night sky in a sledge pulled by reindeer, and enters houses by climbing down chimneys. This strange legend is based on the life of a man called Nicholas, but in fact we know very little about him. Historians think he was a Christian bishop（主教）in Turkey in about 285-350 A.D. One of the stories about him is that he helped three poor girls. No one would marry them because they were so poor.

    To provide them with money for their weddings, Nicholas secretly dropped some gold coins down the chimney of their house. After Nicholas died, he was made a saint（圣人）by the church. (The name Santa Claus thus comes from St Nicholas.) His feast day was celebrated in December, and parents started giving their children secret presents from St Nicholas. Over the years, this custom became part of our Christmas traditions.

    Recently, a psychologist has claimed that Father Christmas is “the perfect fantasy” for children. According to Professor Anthony Clare, children love the character of Father Christmas because he is like an ideal father: he loves children and gives them presents, but he never criticizes them, is never angry and children do not even need to thank him for presents. Other writers, however, point out that Father Christmas can be a frightening character to some children. Jane Bidder says that some children are terrified of this fat, bearded old man. It can certainly confuse many children. As presents, we warn our children to be careful of strangers and never to let them into the house, and yet we tell children that a strange man will come into their bedroom at night! Some children can become very worried about this idea and fear that he is a kind of burglar.

    Most children, however, understand from their parents and from the media that Father Christmas is basically a benign character, and look forward to his annual visit with joy and excitement.

    I have two kids, a boy and a girl. I don't worry about my girl; I'm sure she'll be well trained in mixed martial arts. I worry about my son. I'm pretty sure he's going to be feminine (女性化的). Sorry to say that, but let's face it. No dad wants his son to go feminine.

    At the rate we're moving in a couple of years you won't be able to tell the difference between boys and girls. Sound extreme? Think about this. In every movie where advanced time-traveling beings come to our planet, there's one constant: You can't tell the male aliens from the female aliens!

    But that's the future. Kids today are soft and fat. People ask why. Is it junk food? No. Junk food has been around for fifty years. Is it video games? No. Video games have been around for thirty years. None of the kids playing them back in the day were terribly obese. We're all scratching our heads trying to figure out what we've introduced to society to ruin our kids. But it's not anything we've added that has ruined our kids. It's stuff we've gotten rid of.

    Take the gym rope for example. Remember that thing that stretched from the floor to the ceiling in your gym class that you could never climb? Most of the kids couldn't make it to the top. But that wasn't the point; the point was that you had to try while some middle-aged guy who couldn't make it up a flight of stairs shouted at you. We should have put our son on that rope, and given him a head start. But we didn't want to shame the boy, so we took it down.

    Taking down the rope would be a good idea if there were no ropes in life. But they're everywhere. You just can't see them. They're in every goal unrealized and expectation not met. The point everyone missed about the rope is you weren't supposed to make it to the top. It was there to create a fire that burned in the oversize belly of every kid.

    It's common knowledge that the woman in Leonardo da Vinci's most famous painting seems to look back at observers, following them with her eyes no matter where they stand in the room. But this common knowledge turns out wrong.

    A new study finds that the woman in the painting is actually looking out at an angle that's 15.4 degrees off to the observer's right­well outside of the range that people normally believe when they think someone is looking right at them. In other words, said the study author, Horstmann, "She's not looking at you." This is somewhat ironic, because the entire phenomenon of a person's gaze (凝视) in a photograph or painting seeming to follow the viewer is called the "Mona Lisa effect" . That effect is absolutely real, Horstmann said. If a person is illustrated or photographed looking straight ahead, even people viewing the portrait from an angle will feel they are being looked at. As long as the angle of the person's gaze is no more than about 5 degrees off to either side, the Mona Lisa effect occurs.

    This is important for human interaction with on-screen characters. If you want someone off to the right side of a room to feel that a person on-screen is looking at him or her, you don't cut the gaze of the character to that side­surprisingly, doing so would make an observer feel like the character isn't looking at anyone in the room at all. Instead, you keep the gaze straight ahead.

    Horstmann and his co-author were studying this effect for its application in the creation of artificial-intelligence avatars(虚拟头像) when Horstmann took a long look at the "Mona Lisa" and realized she wasn't looking at him.

    To make sure it wasn't just him, the researchers asked 24 people to view images of the "Mona Lisa" on a computer screen. They set a ruler between the viewer and the screen and asked the participants to note which number on the ruler intersected Mona Lisa's gaze. To calculate the angle of Mona Lisa's gaze as she looked at the viewer, they moved the ruler farther from or closer to the screen during the study. Consistently, the researchers found, participants judged that the woman in the "Mona Lisa" portrait was not looking straight at them, but slightly off to their right.

    So why do people repeat the belief that her eyes seem to follow the viewer? Horstmann isn't sure. It's possible, he said, that people have the desire to be looked at, so they think the woman is looking straight at them. Or maybe the people who first coined the term "Mona Lisa effect" just thought it was a cool name.

    Compared with solar and wind energy, which are booming, tidal (潮汐的) power is a loser in the clean - energy competition. But if you did want to build a tidal power station, there are few better sites than the mouth of the River Severn, in Britain. Its tidal range, the difference in depth between high and low tides, of around 15 metres is among the largest in the world.

    Engineers and governments have been toying with the idea since at least 1925. But none of the suggested projects has materialised. Price is one objection. A study thought that tidal energy might cost between ￡216 and ￡368 ($306 - 521) per MWh of electricity by 2025, compared with ￡58 - 75 for seagoing wind turbines (轮机) and ￡55 - 76 for solar panels. Environmentalists also worry that any plant would change the tides, making life harder for wildlife.

    An engineer called Rod Rainey thinks he has a way around both problems. He plans to replace the conventional turbines of previous plans with a much older technology. Specifically, he plans to span (横跨) the river mouth with a line of water wheels. This is a design that dates back to the early days of the Industrial Revolution. Examples can be found fixed to the sides of old watermills (水磨).

    But there would be nothing old - fashioned about Mr Rainey's wheels. Thirty metres high and sixty wide, they would be made from ordinary steel. Two hundred and fifty of them, along with the supporting structures, would be floated into place and secured to the seabed, creating a line 15km long. Together, they could supply power at an avenge ate of 4GW. That is about as much as two biggish nuclear power stations would manage. Substituting one of the wheels with a set of locks would provide a shipping channel about twice the width of Panama Canal, permitting upstream ports such as Avonmouth and Cardiff to continue operating.

    The negative (负面的) health effects of sleep shortages during the week can't be changed by marathon weekend sleep sessions, according to a new study.

    Researchers have long known that routine sleep deprivation (缺乏) can cause weight gain and increase other health risks, including diabetes. But there are still some people who hope that shutting off the alarm on Saturday and Sunday will repay the weekly sleep debt and remove any ill effects.

    The research, published in Current Biology, ruins those hopes. Despite complete freedom to sleep in and nap during a weekend recovery period, participants in a sleep laboratory who were limited to five hours of sleep on weekdays gained nearly three pounds over two weeks and experienced metabolic disruption (代谢紊乱) that would increase their risk for diabetes over the long term. While weekend recovery sleep had some benefits after a single week of inadequate sleep, those gains were wiped out when people returned right to their same sleep schedule the next Monday.

    "If there are benefits of catch-up sleep, they're gone when you go back to your routine. It's very short-lived," said Kenneth Wright, who led the research. "These health effects are long-term. It's kind of like smoking once was — people would smoke and wouldn't see an immediate effect on their health, but people will say now that smoking is not a healthy lifestyle choice. I think sleep is in the early stage of where smoking used to be."

    Wright said that the study suggests people should prioritize sleep — cutting out the optional "sleep stealers" such as watching television shows or spending time on electronic equipment. Even when people don't have a choice about losing sleep due to child-care responsibilities or job schedules, they should think about prioritizing sleep in the same way they would think about a healthy diet or exercise.