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    Every year, hundreds of millions of Monarch Butterflies(黑脉金斑蝶) from Canada and the United States journey as far as 2, 500 miles to the forests of Michoacan, Mexico, a place which has the world's largest insect migration(迁移). It's such a breathtaking sight, but as always, human greed is threatening to destroy it.

    The Monarch Butterflies start to arrive in Michoacan in late October to make their winter home in the trees high up in the mountains of the natural reserve. Once there, they gather together in large masses. These masses often become so heavy that they cause tree branches to bend or even break. But there's a purpose of all these massing — it allows the butterflies to survive in the low nighttime temperatures at these high altitudes.

    The Michoacan Monarch Butterfly Sanctuary is most impressive during the months of February and March, just before the winged insects begin their long journey home.

    Mexico's Butterfly Forest is a shelter protected by law, and one of the country's most popular sights, but that hasn't stopped people from slowly but steadily destroying it.

    Illegal woodcutting in the heart of the Monarch Butterfly Biosphere Reserve has been a longstanding problem, but criminals are rarely brought to justice. They are often set free after paying some money.

    Just last month, an even greater threat rose in Michoacan's butterfly home.  The country's largest mining corporation gained the right to reopen an old mine in the heart of the monarch reserve. Experts believe that if the mine is reopened, it will likely spell the end of this magical place.

    And as if all this wasn't bad enough, the increasing use of herbicides（除草剂） in the American corn belt has led to the decrease of  a plant which is essential to the monarchs' development from egg into butterfly.

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    LONDON－Scientists have found an unusual way to prevent our planet from overheating: move it to a cooler spot. All you have to do is send a few comets (彗星) in the direction of Earth, and its orbit will be changed too. Our world will then be sent spinning into a safer, colder part of the solar system.

    This idea for improving our climate comes from a group of U. S. National Aeronautics and Space Administration (NASA) engineers and American astronomers. They say their plan could add another six billion years to the useful lifetime of our planet－effectively doubling its working life.

    The plan put forward by Dr. Laughlin, and his colleagues Don Korycansky and Fred Adams, needs carefully directing a comet or asteroid so that it passes close by our planet and sends some of its gravitational energy to Earth.

    “Earth's orbital speed would increase as a result and we would move to a higher orbit away from the Sun,” Laughlin said.

    Engineers would then direct their comet so that it passed close to Jupiter or Saturn. The comet would pick up energy from one of these giant planets. Later its orbit would bring it back to Earth, and the process would be repeated.

    In the short term, the plan provides an ideal way to global warming, although the team was actually concerned with a much greater danger. The Sun is certain to heat up in about a billion years and so “seriously compromise” our biosphere (生物圈) －by cooking us.

    That's why the group decided to try to save Earth.

    The plan has one or two worrying aspects, however. For a start, space engineers would have to be very careful about how they directed their asteroid or comet towards Earth. The smallest miscalculation (误算) in orbit could fire it straight at Earth--with deadly consequences.

    There is also the question of the Moon. As the current issue of Scientific American magazine points out, if Earth was pushed out of its current position, it is “most likely the Moon would be stripped away from Earth”. This would greatly change our planet's climate.

    Imagine a town with crosswalks but no pedestrians, cars and trucks but no drivers. Welcome to Mcity, a fake “city” built by researchers who are testing out the driverless cars of the future.

    The controlled test environment, which opened today (July 20, 2015) at the University of Michigan in Ann Arbor, covers 32 acres (the size of about 24 football fields) and contains all the trappings of a real suburb or small city. There is an entire network of roads lined with sidewalks, streetlights, stop signs and traffic signals. There's even a “downtown” area complete with fake buildings and outdoor dining areas.

    The idea behind Mcity is simple: test out new driverless car innovations in a human-free environment before these technologies are unleashed in the real world.

    "Mcity is a safe, controlled, and realistic environment where we are going to figure out how the incredible potential of connected and automated vehicles can be realized quickly, efficiently and safely," Peter Sweatman, director of the Mobility Transformation Center at U-M, said in a statement.

    The roads of Mcity are built to stand up to “rigorous, repeatable” testing, according to MTC officials. While Mcity drivers don't have to compete with real pedestrians, there will be one mechanical foot-traveler (a robot-like machine named Sebastian) that steps out into traffic to see whether the automated cars can hit the brakes in time. The fake city also features a traffic circle, a bridge, a tunnel, some unpaved roads, and even a four-lane highway with entrance and exit ramps, according to a report by Bloomberg Business.

    In addition to evaluating fully automated, or driverless cars, the researchers also hope to test out so-called connected vehicles within Mcity's limits. Connected cars can either communicate with one another (vehicle-to-vehicle control, or V2V) or with pieces of equipment, such as traffic lights, that are located near roadways (vehicle-to-infrastructure control, or V2I).

    Even the smallest details of Mcity have been planned out in advance to copy the conditions that connected and automated vehicles could face in the real world. For example, there are street signs covered up with graffiti, and faded yellow and white lane markings line the streets.

    Mcity is just one part of a much larger project that MTC and its partner organizations are establishing in an effort to get a whole fleet of connected and driverless cars on the road in Ann Arbor by 2021. In addition to the fake city, MTC is also continuing to launch connected and semi-autonomous(半自动) cars on real roadways. Eventually, the University of Michigan and the Michigan Department of Transportation said they hope to put 20,000 connected cars on the roads of southern Michigan.

    As smog forced students to stay home, the online learning industry saw a sharp increase in consumers.

    During the air pollution red alert from Dec. 8 to 10 last winter, the Beijing Commission of Education ordered all kindergartens, primary schools and middle schools to suspend classes (停课). But the commission urged that, "Teachers should guide students to make full use of digital materials and conduct online learning at home".

    According to the China Education and Research Network, the number of new users of 17zuoye. com, an online homework platform, tripled (增至三倍) on Dec. 8 compared to the previous day.

    Online courses companies also adopted special measures to meet students' demand for Internet learning during the red alert period. For example, New Oriental offered free online English classes for three days for school students as well as online question answering services.

    Recent years have seen the popularity of online courses increase sharply in China. Massive Online Open Courses (MOOC), for example, originated in the United States but have become widespread in China since 2013. Some Chinese universities, including Tsinghua University and Peking University, have started their own MOOC platforms. "MOOCs have enlarged the time and space of teaching, fired up learners' interest, helped more people benefit from high quality educational resources and accelerated reform in many aspects of teaching," an official at the Ministry of Education told China Daily.

    When men and women take personality tests, some of the old Mars-Venus stereotypes(定式)keep reappearing. On average, women are more cooperative, kind, cautious and emotionally enthusiastic. Men tend to be more competitive, confident, rude and emotionally flat. Clear differences appear in early childhood and never disappear.

    What's not clear is the origin of these differences. Evolutionary psychologists think that these are natural features from ancient hunters and gatherers. Another school of psychologists argues that both sexes' personalities have been shaped by traditional social roles, and that personality differences will shrink as women spend less time taking care of children and more time in jobs outside the home.

    To test these hypotheses(假设), a series of research teams have repeatedly analyzed personality tests taken by men and women in more than 60 countries around the world. For evolutionary psychologists, the bad news is that the size of the gender gap in personality varies among cultures. For social-role psychologists, the bad news is that the change is going in the wrong direction. It looks as if personality differences between men and women are smaller in traditional cultures like India's or Zimbabwe's than in the Netherlands or the United States. A husband and a stay-at-home wife in a patriarchal(男权的)Botswanan clan(部族)seem to be more alike than a working couple in Denmark or France. The more Venus and Mars have equal rights and similar jobs, the more their personalities seem to separate.

    These findings are so unbelievable that some researchers have argued they must be due to cross-cultural problems with the personality tests. But according to new data from 40.000 men and women on six continents, David P. Schmitt and his colleagues conclude that the trends are real. Dr. Schmitt, a psychologist at Bradley University in Illinois and the director of the International Sexuality Description Project, suggests that as wealthy modern societies level(使平等)the barriers between women and men, some ancient internal differences are being developed.

    The biggest changes recorded by the researchers involve the personalities of men, not women.

    Men in traditional agricultural societies and poorer countries seem more cautious and anxious, less confident and less competitive than men in the most progressive and rich countries of Europe and North America.

    To explain these differences, Dr. Schmitt and his partners from Austria and Estonia point to the hardships of life in poorer countries. They note that in some other species, environmental stress tends to extremely affect the larger sex. And, they say, there are examples of stress decreasing biological sex differences in humans.

    Scientists recently discovered that pictures on cave walls at Creswell Crags are the oldest known in Great Britain. But they didn't find out in the usual way.

    Archaeologists often date cave art with a process called radiocarbon dating. The technique can measure the age of carbon found in charcoal (木炭) drawings or painted pictures. Carbon is an element found in many things, including charcoal and even people. But in this case, there was no paint or charcoal to test. People carved the pictures of animals and figures into the rock using stone tools. The scientists had an "aha!" moment when they noticed small rocks stuck to the top of the drawings. The small rocks must have formed after the drawings were made.

    "It is rare to be able to scientifically date rock art," said Alistair Pike, an archaeological scientist at Britain's University of Bristol. "We were very fortunate that some of the engravings were covered by stalagmites(石笋).

    When a test proved that the stalagmites formed 12,800 years ago, the scientists knew the art underneath them had to be at least that old. And some of the animals shown, like the European bison, are now extinct-another tip-off that the art is quite old.

    The artists came to Creswell Crags, This place is one of the farthest points north reached by our ancient ancestors during the Ice Age. At that time, much of the North Sea was dry, so people could move about more easily.

    Some tools and bones found there are 13,000 to 15,000 years old. They show that the travelers hunted horses, reindeer, and arctic hare. Their artwork is similar to art in France and Germany. It tells scientists that the Creswell Crags artists must have had a close connection to peoples several thousand kilometers away—another important clue to understanding how humans spread out across the world.