Reflecting(回忆) on the past about those decisions or actions that can't be reversed(推翻) and being occupied with thoughts of “What if?” is no way to live. But there are a few things in life I'd probably do differently if I had the chance.

    I once majored in architecture — something I had been crazy about for as long as I could remember — and then I suddenly had a change of heart. I made an appointment with my adviser, and told him I was no longer certain I wanted to pursue a career in architecture.

    “Don't give up on your childhood dream!” “He's right,” I thought. “I should just stick it out and I shouldn't disappoint the little girl who once loved architecture.”

    It was awful. I was agonized, holding on to a childhood dream that had long since faded. When I talked with a friend about it a year later, he asked: “Right now, what do you want to do with your life?” That's when I came to the realization that dreams change over time and that you should give up the childhood dream if it's not what you want as an adult. Luckily, it wasn't too late. After some serious thought, I changed my major to journalism. It wasn't something I had always imagined myself pursuing — but at that moment,  it was what I wanted.

    We grow up, and sometimes our dreams change — and that's perfectly OK. You just need to ask yourself every once in a while, “Is this still what I want?” If the answer is no, move on and start chasing a new one.

    Six volunteers are about to find out what it would be like to live on Mars without ever leaving the Earth. Three men and three women will spend eight months living in a special place on the side of a volcano in Hawaii. They are part of an experiment that is designed to mimic（模仿）life on Mars. Their mission began on October 15, 2014. NASA says it could send astronauts to Mars as early as the 2030s. The mission would take more than two years, so NASA needs to know how people would react to living in a small group, isolated from the rest of the world, for such a long time. Some people may become depressed or bored living under those conditions. By studying people living in similar conditions here on Eares NASA hopes to learn how to choose the most suitable people for a space mission, and how to help them get along.

    They will live in a two-story building. The ground floor is about 86 square meters, roughly the size of a small two-bedroom apartment. It includes shared areas like kitchen, dining room, bathroom, laboratory and an exercise room. The upstairs is less than half the size of the downstairs. It contains another bathroom and six small bedrooms. The building is located in an abandoned quarry（采石场）about 2,400 meters up the side of Mauna Loa, the second biggest volcano in the world. It is constantly monitored for signs of volcanic activity. NASA chose the location because the appearance looks very similar to Mars.

    To make it more like being on Mars in the future, they are only able to communicate by email during the experiment. Meanwhile, there will be a 20-minute delay between the time when a message is sent and that when it is received. When they go outside, they will have to suit up in full spacesuits, just as if they were on Mars.

    The commander is Martha Lenio, a 34-year-old Canadian. During the mission, she will run experiments on growing food. The other members have backgrounds in physics and so on. None of them are astronauts.

    In 1972, a social worker named Sanjit "Bunker " Roy founded Barefoot College in Tilonia, Rajasthan. Today the college trains women from villages for six months to build and maintain solar panels and other instruments. Barefoot College also offers education to the younger generation both during the day and at its solar bridge schools that meet by lamp light at night.

    The philosophy of the Barefoot College is largely inspired by the principles of Gandhi, starting with quality beyond social classes, sex or religion. As a matter of fact, women are favorably regarded as an underserved population that is necessary to bringing villages together. Another central principle of the college is self-reliance, teaching students to support and think for themselves.

    After the colleges female students have completed their half a year of training, they return to their villages villages, where they wait for solar panel parts to arrive from the college. Once they have all the pieces they need ,they construct the panels and begin collecting solar energy. For each village, the college also provides solar lamps. Villagers can, in addition, order parts for other solar-powered devices, such as water heaters and cooking stoves. Once assembled(组装）, they and the lamps are powered by the solar panels.

    The effect on the villages is huge. Before the solar panels and lamps arrived, villagers had only candles to light their homes. This prevented adults from doing serious work at night, and it made studying difficult for children as well. As for physicians, they have difficulty treating patients and performing operations at night because they had to rely on flashlights.

    Now there is power for not only the electrical appliances that the college provides but also devices like televisions, radios and computers. For the first time, the villagers can even connect to the world through the Internet.

    Two of the saddest words in the English language are if only. I live my life with the goal of never having to say those words, because they convey regret, lost opportunities, mistakes, and disappointment.

    My father is famous in our family for saying, “Take the extra minute to do it right.” I always try to live by the “extra minute” rule. When my children were young and likely to cause accidents, I always thought about what I could do to avoid an “if only” moment, whether it was something minor like moving a cup full of hot coffee away from the edge of a counter, or something that required a little more work such as taping padding (衬垫) onto the sharp corners of a glass coffee table.

    I don't only avoid those “if only” moments when it comes to safety. It's equally important to avoid “if only” in our personal relationships. We all know people who lost a loved one and regretted that they had foregone an opportunity to say “I love you” or “I forgive you.” When my father announced he was going to the eye doctor across from my office on Good Friday, I told him that it was a holiday for my company and I wouldn't be here. But then I thought about the fact that he's 84 years old and I realized that I shouldn't give up an opportunity to see him. I called him and told him I had decided to go to work on my day off after all.

    I know there will still be occasions when I have to say if only about something, but my life is definitely better because of my policy of doing everything possible to avoid that eventuality. And even though it takes an extra minute to do something right, or it occasionally takes an hour or two in my busy schedule to make a personal connection, I know that I'm doing the right thing. I'm buying myself peace of mind and that's the best kind of insurance for my emotional well-being.

    Bats are the only mammals(哺乳动物) that can fly a great distance, but they have another ability. Many bats live a very long time for an animal of their size. European researchers are studying bats to understand why they lives0 long. They hope to make discoveries aimed at fighting the aging process in human beings.

    Last week, the group of scientists said they had identified important biological qualities in some bat species. The group studied bat chromosomes(染色体), a line of genes found in the nucleus(细胞核) of cells. The scientists were most interested in structures connected to the ends of the chromosomes. They are called telomeres(端粒), which protect the ends of chromosomes and shorten each time a cell divides. Scientists believe this shortening process causes cells to breakdown. They say this is what causes aging.

    The European researchers studied 493 bats from four bat species. The group used information that had been gathered over more than 60 years. Of these animals ，the greater mouse-eared bat generally lived the longest, an average of 37 years. The scientists said this and a related species, which are grouped together under the name Myotis, had telomeres that did not shorten with age. Another Myotis bat holds the record for oldest age, reaching 41years. The scientists' findings suggest that these bats cells have the ability to maintain and repair their telomeres. This, they said, helps guard against the aging process.

    Based on its body size, a bat like the greater mouse-eared bat would be expected to live four years. But, these mammals have been found to live nearly 10 times longer than that. The scientists found that only 19 species of mammals live longer than humans when their body size is considered. Eighteen of these are bats.

    Reintroducing beavers (海狸) to Britain could help clean up rivers, prevent flooding and minimise soil loss, an expert has claimed.

    Professor Richard Brazier, a researcher at the University of Exeter, said unpublished results from a trial area in Devon showed muddy water entering an area where beavers were living was three times cleaner when it left. "Our trial has shown that the beavers are able to dam our streams in a way that keeps soil in the headwaters of our catchment (流域) so it doesn't block up rivers downstream and pollute our drinking and bathing waters. If we bring beavers back it's just one tool we need to solve Britain's crisis of soil loss and agricultural pollution of waterways, but it's a useful tool," he said.

    Prof Brazier's claims were disputed by the National Farmers' Union (NFU), which warned that the reintroduction of beavers to Scotland had led to fields and forests becoming damaged. Spokesman Mark Pope said: "The knowledge of the impacts beavers have had on farmland, riverbanks and flood defences in Scotland is concerning. We await the results of the Devon trial and will analyse the outcomes then."

    Prof Brazier, an expert in Earth Surface Processes, insisted the animals could even play a useful role in preventing flooding. He told BBC News: "The public is currently paying people to build leaky dams to keep storm waters in the uplands. The beavers can do it free of charge and even build their own homes."

    However, Professor Jane Rickson, a soil specialist from Cranfield University, Bedfordshire, joined the NFU in sounding a note of caution. She agreed that in some places in the UK there was evidence of worrying soil loss, and said new policies were urgently needed. Beavers may in fact reduce the river channel and remove vegetation, exposing banks to greater erosion (侵蚀) and increasing, rather than decreasing, the risk of flooding, she warned. And she said beaver dams should be "leaky" to avoid build-ups of large volumes of water.