Traffic problems are an everyday concern in many cities, including Washington, D. C. A growing number of Washingtonians are turning to bicycles to get to and from work. In fact, the number of commuters who use bicycles has doubled in the city since 2007.

    Ralph Buehler teaches urban planning at the Virginia Polytechnic Institute and State University，popularly known as Virginia Tech. He has written a book about urban biking, called City Cycling. He says there is a reason why urban bike tiding is now becoming more popular.

    “Over the last 60 to 70 years, cities in America have been adapted to the automobile.”

    “Most cities took advantage of the money coming for the interstate (洲际)highway system, from the federal government, starting in 1956. There was a 90 percent federal match(补贴)so the cities only had to put up 10%. It was very tempting.(临时的).”

    In the years after World War Two, many Americans moved to suburban communities, just outside major cities, They decided to travel great distances to and from work in exchange for a home in the suburbs. Their cars became a symbol of freedom.

    But today, many people believe they can save money by living in the city.

    Greg Billing is with the Washington Area Bicyclist Association. “When a person makes a change from using a car to using a bike, he/she is saving anywhere between 8 or$9,000 a year.”

    Ralph Buehler says governments save money when people use bicycles. “Building bicycling facilities(设施) is much cheaper than building and maintaining road facilities or public transport.”

    Washington, D.C has also taken steps to protect bike riders. It approved a safe passing law and created areas on the road between cars and bikes.

    The United States Census Bureau says 4% of the city's workers ride to work by bike. The only city on the East Coast with more bike commuters is New York.

    Customers who come into the Waffle House recognize server Evoni Williams, a soft-spoken 18-year-old from Texas City. It all started with a Facebook post. On the morning of March 3, Laura Wolf was eating breakfast at the Waffle House in La Marque when she overheard an older man, who reminded her of her late father, tell Williams he had trouble with his hands. The man, later identified as regular customer Adrien Charpentier, had an oxygen tank nearby and needed help cutting up his food. “Without hesitation,” Wolf wrote, Williams “took his plate and began cutting up his ham.”

    Impressed, Wolf posted the moment on her Facebook page to share the warmth and kindness with all. The following day, Williams's Facebook notification（关注）began to light up. Her friends saw Wolf's post and tracked her in it.

    Williams had no idea that someone took a photo that morning. The diner was so busy that a line extended outside the door. She said helping Charpentier was reflexive. She has been working at Waffle House since last June to save for college, and this, she figured, was just the right thing to do. “I would want someone to help my grandmother or grandfather,” Williams said.

    The post began to make its rounds in La Marque and eventually landed in front of the city's mayor, Bobby Hocking. He decided to declare March 8 as Williams's day, and also received an email from Texas Southern University President Austin A.Lane, asking if the school could present Williams with a scholarship.

    Williams still works at Waffle House five days a week and plans to do so until she starts classes in the fall at Houston-based Texas Southern. Wolf said Williams does not have a car to get to classes, but some people have offered to start a GoFundMe page for her, proving that a moment of a kindness can change a life.

    A new study suggests climate conditions in the Sahara Desert, one of hottest, driest and most deserted areas in the world, have changed from wet to dry a about every 20,000 years.

    But previous evidence has suggested the Sahara did not always experience such extreme heat and dry conditions. At times, the Sahara Ranged to a very wet climate. This permitted plants and animals to develop and grow and led to the creation of human settlements. Now, they have discovered more evidence, which, the lead researcher David Mc Gee says, supports the idea that the Sahara's climate kept changing between wet and dry about every 20,000, years.

    McGee reported these climate changes were mainly driven by changes in the Earth's(地轴)as the planet travels round the sun .This process affects the amount of sunlight between seasons. Every 20,000 years the Earth receives more strong summer sunlight. When the Earth's axis changes again, the amount of sunlight is reduced. This season change happened continuously every 20,000 years. The other part of the season produced rainy conditions, resulting in a wetter, greener, plant-rich environment. When the rainy activity weakens, the climate becomes hot and dry, like the Sahara remains today.

    The scientists based their research on dust collected from ocean sediment(沉积物)in the Atlantic Ocean bottom off the coast of West Africa. The dust contained layers (层)of ancient sediment built up over millions of years. Each layer could contain traces of Saharan dust as well as the remains of life forms. This information was used to assess over what time period the dust had built up. This led to the overall finding that the Saharan changes from wet to dry climates happened every 20,000 years.

David McGee said that today we only see the Sahara Desert as an extremely deserted and "inhospitable" place. The new study suggests that the area's climate has changes between grasslands and a much wetter environment, and back to dry climates, even over the last quarter million years. McGee says he thinks the latest research can be valuable in studying the Sahara's history as it relates to human settlement.

    A good disguise keeps you hidden, right? Well, sometimes the best disguise is actually the most dazzling because research reveals that flashy metallic iridescence(金属彩虹色) can visually puzzle predators, which allows colorful prey to survive another day. Those surprising results appear in the journal Scientific Reports.

    Shining iridescent color, which changes depending on the angle from which it's viewed, is favored by everything from birds to beetles and blossoms to butterflies.

    "And in our research group we are of course interested in why this vivid metallic color is so widespread in nature." Karin Kjernsmo of the University of Bristol adds that in some cases the showy splashes of light are a sexual strategy. " Here I would like to point out that in some species, particularly those that display strong sexual dimorphism(雌雄两性), such as birds of paradise or some butterflies or fishes, the occurrence of iridescence is most likely driven by sexual selection. For example, in many of these cases it is the males that have these vivid iridescent colors and they use them in mate choice or they use them as a signal to attract mates."  But iridescence also shows up in situations where reproduction is not an issue. " So what we are studying now is whether natural selection imposed by predation(捕食行为) could explain the occurrence of iridescence in prey animals."

    The idea that eye­catching colors could be used as a cover­up isn't a new one." The father of camouflage theory, Abbott Thayer, really believed that iridescence should be categorized as a camouflage strategy. And he wrote in his famous lifework Concealing­Coloration in the Animal Kingdom, already in 1909, that 'brilliantly changeable or metallic colors are among the strongest factors in an animal's concealment'. And this sounds like a completely unreasonable thing to say, because how can colors that are both brilliant and changeable contribute to animal's concealment？"

    "In a similar way, we were asking whether iridescence, due to its changeability, could work as a form of camouflage by preventing shape recognition." Kjernsmo and her colleagues trained bumblebees to associate a particular shape—a circle or an oval—with a sugar reward. And they found that the bees, when given a choice, would preferentially visit the shape they knew to be sweet. But when the shapes were iridescent, the bees had trouble telling them apart. "It seemed that the strikingly iridescent surfaces on our targets visually broke up the otherwise recognizable shape of the targets, which made them hard to distinguish." As for making use of this method for hiding in plain sight, "Any practical applications is of course directly linked to any industry that has an interest in camouflage, that is how to conceal objects or make them more difficult to recognize." The researchers are currently conducting experiments with birds, which often prey on iridescent insects to see if it helps to have a bird's­eye view.

    David Rees runs a truly distinctive business. He charges customers $15 to shar pen their pencils to perfections, using a variety of tools.

    I know what you're thinking — is this a joke? The 39-year-old gets asked that question a lot. To clarify everything, he even created a special section on his website telling everyone he's actually providing a real service.

    You can supply your own pencil or you can have Rees sharpen one of his own favorite 2B pencils. After that, he mails it to you in a display tube with the shavings in a separate bag, and an authentic certificate which just happens to mention the pencil is so sharp as to be a dangerous object.

    To achieve the desired result, the master sharpener uses all kinds of tools, including general sandpapers, pocket knives and even a special $450 sharpening machine. "It depends on what the customer wants to use his/her pencil for," he says. "That determines the most appropriate pencil-sharpening technique.

    Some customers buy pencils as inspirational symbols while others buy them because of their special memories of classic 2B pencils.

    $15 to have a pencil sharpened is a bit expensive though, right? You're not the only one who feels that way, and David's unique business has really angered lots of people, who talk of inequality in America, saying it is so insane for the wealthy to pay $15 to sharpen a pencil. But others will say, "This is just our urge to put an end to the welfare state because new ideas arise along with the business."

    David admits his trade is sort of unusual. But there are those who actually value his service, as proven by the over 500 orders he has gotten.

The summer I turned 16, my father gave me his car — a gift wasted on me at that age. The important thing was that Hannah and I could drive around.

    Hannah was my best friend, a year younger but much taller, almost five foot ten. "Hannah's a knockout," my mother always said. And that summer she signed with a modeling agency. She was already doing runway work.

    A month after my birthday, Hannah and I went to the movies. On the way home, we stopped at the McDonald's drive-through, putting the fries on the seat between us to share. "Let's ride around a while," I said. It was a clear night, full moon slung low over the desert. Taking a turning too fast, I plowed (撞)through a neighbor's wall and drove into a full-grown tree.

    We were taken in separate ambulances. I'd cracked(使裂开)my cheek bone; Hannah's forehead had split wide open. End of her modeling career. What would I say to her?

    When her mother, Sharon, came into my hospital room, I started to cry. She sat beside me and took my hand. "I rear-ended(追尾) my best friend when I was your age, "she said, "I totaled her car and mine."

    "I'm so sorry." I said.

    "You're both alive," she said, "The rest is window dressing. I forgive you. Hannah will too."

Sharon's forgiveness allowed Hannah and me to stay friends throughout high school and college, to be at each other's weddings … The scars are so faded that no one else would notice, but in the sunlight I can still see it just below her hairline — for me, a mark of grace(优雅).