According to sociologists(社会学家), every modern industrial society has some form of social stratification(阶层). Class, power and status are important in deciding people's rank in society.

    Class means a person's economic position in society. A commonly used classification is lower class, middle class and upper class. While sociologists disagree on how these terms should be exactly defined, they do describe societies like the United States quite well. One study shows that 53% of Americans belong to the lower class, 46% the middle class, and 1% the upper class. Interestingly, a surgeon earning $500,000 a year and a bus driver earning $50,000 a year both regard themselves as the middle class!

    Power refers to the amount of control a person has over other people. Obviously, people in positions of great power (such as governors) exercise(行使)big power, but people who take orders from others have less power. Power and class do not always go hand in hand, however. For example, the governor of a state has great power, but he or she may not belong to a corresponding (相应的)economic class. Generally, however, there is a relationship between power and class. To our knowledge, there aren't too many people who aren't millionaires in the U．S. Senate!

    Status is the honor or respect attached to a person's position in society. It can also be affected by power and class, but not necessarily so. For example, a university professor may have a high status but not belong to a high social class or have a lot of power over others.

    The year 3700, Earth is far too hot for any human to call it home. On this planet at least, man is nothing more than a memory--if there is anything left to remember the "wise man". But what about our wisdom--will any of it survive us?

    The conventional answer is no. Knowledge requires a knower, and there will be no knowing minds around then. But if information survives, perhaps in books or hard drives, maybe the knowledge isn't quite dead but dormant(休眠), ready to become alive with the help of other minds that develop over time or come to visit Earth in the distant future.

    At first sight, that seems to be reasonable: after all, we have done similar things with past knowledge. For example, we saved an ancient computer from a ship destroyed at sea off the southern coast of Greece, and succeeded in finding the meaning of Egyptian hieroglyphics(象形文字). Careful work can bring previously lost wisdom back to life.

    However, the key point is that there is a certain cultural continuity with those ancient times that allows us to reason and make progress in the dark: we know we are dealing with the legacy(遗产)of other humans. Without that link, the survival of objects and raw data doesn't guarantee the survival of knowledge. And a lack of continuity in language with any future intelligence would be a barrier. Knowledge is closely connected with language. When a language dies out, we can lose systems of reasoning that they contain. If that's lost, then it can't be recovered.

    All this means that other minds might not be able to fully make human knowledge alive when we are gone. It is better to concentrate on not dying out in the first place.

    About three decades ago, China was known as the “Bicycle Kingdom”. But later on, bikes were replaced by their fuel-powered competitors.

    But recent months have seen a recovery of the humble bike across China, with an increasing number of people choosing cycling instead of driving to schools, to workplaces or to do sightseeing. The introduction of bike-sharing schemes, pioneered by start-ups like Ofo and Mobike, has brought the trend to a new level.

    People can unlock the shared bikes by simply using their smart phone. The bikes are equipped with GPS and can be left anywhere in public for the next user. They're popular among many Chinese people as they provide an effective solution to the “last mile” problem, which refers to the final leg of a person's journey.

    “In places where the subway doesn't extend, where it's difficult to change from one kind of transport to another, it's so easy to get where you want to go with Mobike,” Hu Hong. 29, told AFP. She pedals（骑车）to her Shanghai real-estate job.

    However, the schemes have also led to problems such as illegal parking, vandalism（故意毁坏）and theft. Last month, two nurses in Beijing were placed under administrative punishment for five days for putting locks on two shared bikes. And in December, a man who stole a shared bike was sentenced to a 3-month detention（拘留）, and fined 1,000 yuan by the Shanghai Minhang People's Court.

    “Bike-sharing is a greener method of transportation and provides a user-friendly experience.” said Liu Xiaoming, vice-minister of transport.

    “But it's a combination of online and offline business. Operators are usually strong in online services, but lack offline business experience, which causes problems.”

    In earliest times, men considered lightning to be one of the great mysteries (神秘的事物)of nature. Some ancient peoples believed that lightning and thunder were the weapons (武器) of the gods.

    In reality, lightning is a flow of electricity formed high above the earth. A single flash of lightning 1.6 kilometres long has enough electricity to light one million light bulbs (灯泡).

    The American scientist and statesman, Benjamin Franklin, was the first to show the connection between electricity and lightning in 1752. In the same year he also built the first lightning rod (避雷针). This device (装置物) protects buildings from being damaged by lightning.

    Modern science has discovered that one stroke (闪击) of lightning has a voltage (电压) of more than 15 million volts (伏特). A flash of lightning between a cloud and the earth may be as long as 13 kilometers, and travel at a speed of 30 million meters per second.

    Scientists judge that there are about 2,000 million flashes of lightning per year. Lightning hits the Empire State Building in New York City 30 to 48 times a year. In the United States alone it kills an average (平均数) of one person every day.

    The safest place to be in case of an electrical storm is in a closed car. Outside, one should go to low ground and not get under tress. Also, one should stay out of water and away from metal fences. Inside a house, people should avoid open doorways and windows and not touch wires or metal things.

    With lightning, it is better to be safe than sorry?

The teenage Snowboarder.

I was born in Denver, USA. and started snowboarding aged eight when my dad took me to a resort in the mountains. About two hours from Denver. The hill looked unbelievably steep and scary. So My dad had to do a lot of persuading to get me on a board. Because I was so young. I hadn't even thought of asking him if I could start snowboarding? But he was already into it and wanted me to love it, too—-He made it look so simple, and in the end I managed just fine.

After this experience, it wasn't long before I'd developed a love of sport and had improved my ability too. I started competing aged ten. Some people entered loads of competitions and ended up getting bored of snowboarding. But my love of taking part and winning got stronger as I got older, which always help me to push myself harder. I enjoyed not having a fixed plan and sometimes this went well, like when I became the first female ever to get a perfect 100 at a local competition. I wasn't sure I'd even attempted the jumps that got me the score until I actually set off. That achievement increased my trust in my own abilities.

During the summer I focused on training and my studies while there's no snow. Although I trained daily, it's nice not having to stick to quite a strict diet like I did in the winter. I also got to spend lots of time with my friends then. It's the best way of dealing with not being able to do what I loved so much and what I was really good at.

Now. I have to think carefully about my future. Snowboarding is such a huge part of my life now. But I also feel it's important to have something else I can do. just in case I don't succeed as a professional snowboarder or I get injured. I'm wondering whether becoming a doctor is a possibility. if my active life allows time for doing a college degree, it's impossible to imagine myself growing tired of the sport. But I can't go on snowboarding my whole life.