Hummingbirds(蜂鸟) are one of nature's most energetic fliers and the only birds to hover(盘旋) in the air by relying on their strength alone.

    Now scientists have found that it is the ratio(比值) of the bird's wing length to its width that makes them so efficient. The discovery is helping experts compete with 42 million years of natural selection to build helicopters that are increasingly efficient.

    David Lentink, an assistant professor at Stanford University in California, tested wings from 12 different species of hummingbirds, which he sourced from museums. He placed them on a machine used to test the aerodynamics(气力学) of the helicopter blades(桨叶). Professor Lentink's team used the same machine to test the blades from an advanced micro-helicopter used by the UK's army. They found that the micro-helicopter's blades are as efficient at hovering as the average hummingbirds.

    But while the micro-helicopter's blades kept pace with the average hummingbird wings, they could not keep up with the most efficient hummingbird's wing. The wings of Anna's hummingbird were found to be about 27 percent more efficient than the man-made micro- helicopter's blades.

    While Professor Lentink wasn't surprised at nature's superiority, he said that helicopter blades have come a long way. “The technology is at the level of an average hummingbird,” he said. “A helicopter is really the most efficient hovering device that we can build. The best hummingbirds are still better, but I think it's amazing that we're getting closer. It's not easy to match their performance, but if we build better wings with better shapes, we might match hummingbirds.”

    Professor Lentink said that we don't know how hummingbirds maintain their flight in a strong wind, how they navigate(确定方向) through branches, or how they change direction so quickly. He thinks that great steps could be made by studying wing aspect ratios-the ratio of wing length to wing width. Understanding these abilities and characteristics could be a benefit for robotics and will be the focus of future experiments.

根据短文内容，选择最佳答案，并将选定答案的字母标号填在题前括号内.

    Human brains begin growing and developing at a very young age. They learn from the simplest experiences, which enable your children to be aware of the world. There's no denying that outdoor play helps a lot!

Times when children have to wait for their turns on playground equipment and following the playground rules by sharing, all these form components of a healthy social-emotional development. Young children develop their social-emotional skills through practice and small steps over time.

As parents or caregivers, it is fairly simple to support your child's social-emotional skills. Acts like holding him, touching him, and speaking to him and giving him loving care and attention are all helping factors. When you allow them freedom to play, it is important to follow their interests in helping build their social-emotional skills.

Difficulties in social-emotional skills can often lead to children having trouble when playing with other children. Becoming easily angry or not empathizing (理解) with other children are all signs that may point in this direction. This can in turn lead to them not empathizing with the needs of other children.

    As for the development of cognitive (认知的) skills, these develop through practice and opportunity over time. And while some cognitive skills may be genetic, most are learned through real life situations. In other words, learning and thinking skills can be improved through experiences.

    To enable them to learn, it is important that we are mindful of what our children are interested in. And this realization is only set in place once the child is given enough room and time to grow and explore.

    Depriving children of such experiences can mean that they might struggle with higher- level thinking skills. And while it is normal to keep them safe, we forget that by rushing them and cutting down on play time, we're actually causing more harm than good.

    That people often experience trouble sleeping in a different bed in unfamiliar surroundings is a phenomenon known as the 4Tirst-nighf, effect. If a person stays in the same room the following night they tend to sleep more soundly. Yuka Sasaki and her colleagues at Brown University set out to investigate the origins of this effect.

    Dr. Sasaki knew the first-night effect probably has something to do with how humans evolved.

    The puzzle was what benefit would be gained from it when performance might be affected the following day. She also knew from previous work conducted on birds and dolphins that these animals put half of their brains to sleep at a time so that they can rest while remaining alert enough to avoid predators (捕食者). This led her to wonder if people might be doing the same thing. To take a closer look, her team studied 35 healthy people as they slept in the unfamiliar environment of the university's Department of Psychological Sciences. The participants each slept in the department for two nights and were carefully monitored with techniques that looked at the activity of their brains. Dr. Sasaki found, as expected, the participants slept less well on their first night than they did on their second, taking more than twice as long to fall asleep and sleeping less overall. During deep sleep, the participants' brains behaved in a similar manner seen in birds and dolphins. On the first night only, the left hemispheres (半球) of their brains did not sleep nearly as deeply as their right hemispheres did.

    Curious if the left hemispheres were indeed remaining awake to process information detected in the surrounding environment, Dr. Sasaki re-ran the experiment while presenting the sleeping participants with a mix of regularly timed beeps (蜂鸣声) of the same tone and irregular beeps of a different tone during the night. She worked out that, if the left hemisphere was staying alert to keep guard in a strange environment, then it would react to the irregular beeps by stirring people from sleep and would ignore the regularly timed ones. This is precisely what she found.

    Tiny microbes(微生物)are at the heart of a new agricultural technique to manage harmful greenhouse gas. Scientists have discovered how microbes can be used to turn carbon dioxide into soil­enriching limestone(石灰石), with the help of a type of tree that grows in tropical areas, such as West Africa.

    Researchers have found that when the Iroko tree is grown in dry, acidic soil and treated with a combination of natural fungi(霉菌)and other bacteria, not only does the tree grow well, it also produces the mineral limestone in the soil around its root.

    The Iroko tree makes a mineral by combining Ca from the earth with CO₂ from the atmosphere The bacteria then create the conditions under which this mineral turns into limestone. The discovery offers a new way to lock carbon into the soil, keeping it out of the atmosphere. In addition to storing carbon in the trees leaves and in the form of limestone, the mineral in the soil makes it more suitable for agriculture.

    The discovery could lead to reforestation(重新造林) projects in tropical countries, and help reduce carbon dioxide in the atmosphere in the developing world. It has already been used in West Africa and is being tested in Bolivia, Haiti and India.

    The findings were made in a three­year project involving researchers from the Universities of Edinburgh, Granada, Lausanne and Delft University of Technology. The project examined several microbiological methods of locking CO₂ as limestone, and the Iroko­bacteria way showed best results. Work was funded by the European Commission under the Future&Emerging Technologies(FET)scheme.

    Dr. Bryne Ngwenya of the University of Edinburgh's School of GeoSciences, who led the research, said: "By taking advantage of this natural limestone­producing process, we have a low­tech, safe, readily employed and easily operating way to lock carbon out of the atmosphere, while improving farming conditions in tropical countries."

The recent few weeks have been the perfect time for a good book and here are some good ones that allow readers to get completely lost in another world.

Watch Me Disappear

If you like mysteries with family drama, Janelle Brown's best-selling thriller is for you, The story follows a wealthy wife and mom who goes on a hike and never returns. Her lonely husband and teenage daughter, Olive (who's dealing with her own problems), are confused with sorrow while trying to find out what happens.

The Boy from the Woods

If you pick up one of Harlan Coben's books, you won't be able to put it down. His misty stories keep readers fascinated. The Boy from the Woods, is sure to satisfy fans of his twisty, heart-racing plots filled with interesting and exciting atmosphere. This is the book to read if you love masterful surprises.

How to Walk Away

Katherine Center's best-selling novel follows a young woman, Margaret, with her perfect fiance, a pilot who takes her on a upsetting flight that changes her life forever. Readers adore Margaret's wisdom and humor as she faces a changed world and figures out what love really looks like.

The Last One Left

This novel, first published in 1967, still attracts readers decades later. Novelist Dean Koontz wrote the introduction to the recent edition, where he describes reading each of John D. MacDonald's novels" at least three times, some of them twice that often. "This is your next read if you want to be swept away by a master of mystery and excitement.