How fit are your teeth? Are you lazy about brushing them? Never fear: An inventor is on the case. An electric toothbrush senses how long and how well you brush, and it lets you track your performance on your phone.

    The Kolibree toothbrush was exhibited at the International Consumer Electronics Show in Las Vegas this week. It senses how it is moved and can send the information to an Android phone or iPhone via a Bluetooth wireless connection.

    The toothbrush will be able to teach you to brush right (don't forget the insides of the teeth!) and make sure you're brushing long enough. “It's kind of like having a dentist actually watch your brushing on a day-to-day basis,” says Thomas Serval, the French inventor.

    The toothbrush will also be able to talk to other applications on your phone, so developers could, for instance, create a game controlled by your toothbrush. You could score points for beating monsters among your teeth. “We try to make it smart but also  fun,” Several says.

    Serval says he was inspired by his experience as a father. He would come home from work and ask his kids if they had brushed their teeth. They said “yes,” but Serval would find their toothbrush heads dry. He decided he needed a brush that really told him how well his children brushed.

    The company says the Kolibree will go on sale this summer, for $99 to $199, developing on features. The U.S. is the first target market.

    Serval says that one day, it'll be possible to replace the brush on the handle with a brushing unit that also has a camera. The camera can even examine holes in your teeth while you brush.

    However wealthy we may be, we can never find enough hours in the day to do everything we want. Economics deals with this problem through the concept of opportunity cost, which simply refers to whether someone's time or money could be better spent on something else.

    Every hour of our time has a value. For every hour we work at one job we could quite easily be doing another, or be sleeping or watching a film. Each of these options has a different opportunity cost—namely, what they cost us in missed opportunities.

    Say you intend to watch a football match but the tickets are expensive and it will take you a couple of hours to get to and from the stadium. Why not, you might reason, watch the game from home and use the leftover money and time to have dinner with friends? This—the alternative use of your cash and time—is the opportunity cost.

    For economists, every decision is made by knowledge of what one must forgo—in terms of money and enjoyment—in order to take it up. By knowing precisely what you are receiving and what you are missing out on, you ought to be able to make better-informed, more reasonable decisions. Consider that most famous economic rule of all: there's no such thing as a free lunch. Even if someone offers to take you out to lunch for free, the time you will spend in the restaurant still costs you something in terms of forgone opportunities.

    Some people find the idea of opportunity cost extremely discouraging: imagine spending your entire life calculating whether your time would be better spent elsewhere doing something more profitable or enjoyable. Yet, in a sense it's human nature to do precisely that—we assess the advantages and disadvantages of decisions all the time.

    In the business world, a popular phrase is “value for money.” People want their cash to go as far as possible. However, another is fast obtaining an advantage: “value for time.” The biggest restriction on our resources is the number of hours we can devote to something, so we look to maximize the return we get on our investment of time. By reading this passage you are giving over a bit of your time which could be spent doing other activities, such as sleeping and eating. In return, however, this passage will help you to think like an economist, closely considering the opportunity cost of each of your decisions.

    This may be music to your ears.

    Researchers P. Jason Rentfrow and Samuel Gosling gave 3,500 people a personality quiz. “We found that the musical styles people like are closely linked to their personalities,” Gosling says.

    RAP/HIP-HOP

    Known for their quick speech, some rappers can say more than 700 syllables（音节）a minute!

    If you like rap/hip-hop, you are energetic（精力充沛的）and have a way with words. You put a fresh spin on things, whether it's new moves on the dance floor or your hip style.

    CLASSICAL

    In the 18th century, classical musicians were like rock stars. Beethoven and Mozart, for example, played in crowded concert halls.

If you like classical, you are open to new ideas and like debating with friends. Creative and imaginative, you can easily spend many hours scrapbooking, writing or painting.

    COUNTRY

    Country music came from the folk songs of English, Scottish, and Irish settlers of the southeastern United States.

    If you like country, you express your opinions well, which makes you the ideal class president or team captain. Traditional and loyal, you enjoy spending time with your family.

    POP

    Pop music is designed to attract almost everyone, and it does. Each year, the industry brings in about 30 billion dollars!

    If you like pop, you are attractive to your friends. You can make big things happen, like planning for a huge party or inspiring your team to victory.

ROCK/ALTERNATIVE

    In the 1950s, rock music created a brand-new culture. Teenagers, for the first time, had an identity separate from adults and children.

    If you like rock/alternative, you are a risk-taker who never accepts no for an answer. You rise to any challenge, like doing very well in a big exam or landing the lead in the school play.

    If these personality profiles（人格剖析）don't match you, that's OK. These are just for fun.

    The month of March was a milestone for supporters of renewable energy in the U.S. For the first time, wind and solar power accounted for more than 10% of the country's electricity—up from less than 1% at the turn of the century. And total wind and solar power-plant capacity(发电量) is expected to grow more than 30% over the course of this year and next, according to the Energy Information Administration.

    Such forecasts have led many scientists and policymakers to think that moving a large part of the nation's power supply to renewable sources—as cities from Miami Beach to Salt Lake City have promised to do—may not be as far-fetched as once thought. But like any debate, there are dissenters, including those inside the federal government. Their argument is that the nation demands an uninterrupted supply of electricity and cannot count on sun, wind and natural gas to provide it. “You need solid hydrocarbons(固体碳氢化合物) on-site for rising peak demand,” Environmental Protection Agency administrator Scott Pruitt said on Fox Business in May, referring to the importance of coal as a power source.

    Many experts say the government's concern fails to account for how the power grid(电网) has improved in recent decades. Utility companies(公共事业公司) have developed innovative ways to move electricity from place to place to account for variation in weather. Battery technology can store power for use when renewable sources cannot operate, meaning solar power can be used on days when the sun doesn't shine. And the nation's vast supply of natural gas can be turned into usable energy with the flick of a switch.

    “I don't think 5 or 10 years ago I'd be comfortable telling you we could not sacrifice reliability when we're going to have 35% of our energy come from wind,” said Ben Fowke, CEO of the utility company Xcel Energy, at a recent conference. “I'm telling you, I'm very comfortable with that today.”

    Indeed, many parts of the country are already close to that reality. In some regions, like Iowa and Kansas, renewable energy supplies more than 25% of the electricity. The market has shifted so far in favor of natural gas and renewable energy that even the most concerted federal effort is unlikely to stop its growth. Any attempt to slow the growth of wind and solar will face strong pushback. “If anyone wants to do away with it,” Republican Senator Chuck Grassley told Yahoo News of the federal government's potential cuts to wind energy, “he'll do it over my dead body.”

    But the federal government could slow the acceleration—and with billions of dollars in private and public investments at risk, the pace of change matters. Decisions made today will shape the future of the nation's energy grid for decades to come.

    In a big room on the second floor of the New York City Department of Sanitation's East 99th Street garage, 63-year-old Manhattan native Nelson Molina was listening to a Frank Sinatra CD he found in the trash. "The Way You Look Tonight" was playing through a music player. In fact, the entire space was filled with items strangers threw away. "My family kept everything," said Molina. "Nowadays, people throw it all away." Molina, during his 34 years as a sanitation worker （环卫工人）, gave these items a second life.

    Molina grew up in a housing project with his parents and five other kids in the family and had a habit of picking up unused items at a young age. "My family was poor, so we didn't get much for Christmas," he said. "I'd go out to look for a toy for my sisters, maybe a truck for my brothers." He kept his early morning habit secret from his friends, but not out of embarrassment: "I didn't want the competition."

    On the job, Molina had his sixth sense for finding items. "I could tell, sometimes just by the sound, whether a bag was filled with bottles or a different kind of glass," he said. He kept special finds on the truck, and then put them in out-of-the-way places in the sanitation garage. After almost 10 years, he began showing his discoveries. "It's not a normal practice." said NYC Department of Sanitation assistant chief Keith Mellis. Recently, a team of New York University students has taken on the task of cataloging （分类） the tens of thousands of objects, in hopes that the collection, which has hardly been open to the public, might one day be shown in an official sanitation museum.

    We have encountered a crisis around the corner. You mean global warming? The world economy? No, the decline of reading. People are just not doing it anymore, especially the young. Who's responsible?

Actually, it's more like, what is responsible? The Internet, of course, and everything that comes with it – Facebook, Twitter. You can write your own list.

    There's been a warning about the imminent death of literate civilization for a long time. In the 20th century, first it was the movies, then radio, then television that seemed to spell doom for the written world. None did. Reading survived; in fact it not only survived, it has flourished. The world is more literate than ever before – there are more and more readers, and more and more books.

    The fact that we often get our reading material online today is not something we should worry over. The electronic and digital revolution of the last two decades has arguably shown the way forward for reading and for writing. Take the arrival of e-book readers as an example.

    Devices like Kindle make reading more convenient and are a lot more environmentally friendly than the traditional paper book.

    As technology makes new ways of writing possible, new ways of reading are possible. Interconnectivity allows for the possibility of a reading experience that was barely imaginable before. Where traditional books had to make do with photographs and illustrations, an e-book can provide readers with an unlimited number of links: to texts, pictures, and videos. In the future, the way people write novels, history, and philosophy will resemble nothing seen in the past.

    On the other hand, there is the danger of trivialization. One Twitter group is offering its followers single-sentence-long "digests" of the great novels. War and Peace in a sentence? You must be joking. We should fear the fragmentation of reading. There is the danger that the high-speed connectivity of the Internet will reduce our attention span—that we will be incapable of reading anything of length or which requires deep concentration.

    In such a fast-changing world, in which reality seems to be remade each day, we need the ability to focus and understand what is happening to us. This has always been the function of literature and we should be careful not to let it disappear. Our society needs to be able to imagine the possibility of someone utterly in tune with modern technology but able to make sense of a dynamic, confusing world.

    In the 15th century, Johannes Guttenberg's invention of the printing press in Europe had a huge impact on civilization. Once upon a time the physical book was a challenging thing. We should remember this before we assume that technology is out to destroy traditional culture.