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.

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    Proper diet and regular exercise seem to be the only methods for losing weight.However,the importance of water should be added in the process.While medical science has proven the positive effects of water,most people still do not drink enough each day.

    The reason why water is so important for weight loss has something to do with metabolism（新陈代谢）of fat. The liver（肝脏）is in charge of this process when it comes to turning stored fat in-to energy.However,the liver is also responsible for helping the kidneys（肾脏）that need enough water in order to function properly.The liver has to perform all the functions of the kidneys on its own when they are short of water.This means the liver doesn't have enough energy to metabolize fat.So,drinking water allows the kidneys to focus on their job and the liver to focus on its job.

    Also,studies have shown that water can make us feel full when drunk before meals.Without even making an effort,most people who drink a glass of water before a meal will eat 33% less.This is due in part to the fact that they simply get fuller quicker because the water is taking up space.The other reason is that the food will expand as soon as it hits the water-filled stomach.

    Water is important for every aspect of the health of the human body.By drinking more water and improving the health of the body,weight loss goals can be achieved with greater ease.

    Most people know that listening to music when they are feeling down or depressed can encourage their spirits.

    However studies have also shown that music, especially certain tones can reduce stress. Music can change brainwave patterns, deepen breathing, and bring on a totally stress-free and more open mindset（心态）. Using music to relax when considering a particular problem may not only raise your mood, but also could help you reach that "a-ha"moment and find a solution.

    Music has also been shown not only to make you feel good, but also, to be a great motivator. For example, during exercise, listening to music can keep you going, or get you to exercise more by helping you to ignore negative feelings of tiredness and focus on the pleasurable feelings you get from being absorbed in the music.

    Music is mainly used to record emotion. When we listen to a piece of music we share the artist's feelings on a visceral（本来的）level. That can be sad, and who among us hasn't put on a painful love song to share in the misery after a bad break-up? On the contrary, we can share in the delight of songs of joy and happiness, or any song or piece of music that reminds us of a particular happy time in our past.

    So next time you are feeling down, put on Beethoven' s Ode to Joy, I bet you will feel a lot better about whatever it was that was bothering you!

    Many people wrongly think that cities don't have farms and fruits and vegetables are only grown in the country. Believe it or not, there are more urban farms popping up in cities all over the world.

    Alexandra Sullivan, a food systems researcher in New York, studies urban agriculture. Urban agriculture is another name for farming and gardening in a city environment. Ms. Sullivan studies everything from tiny gardens in empty lots between buildings to bigger fields that have been planted and grown. According to Ms. Sullivan, “Urban agriculture has existed since cities have, across the world.”

    The number of humans living in urban areas, or cities, is increasing. The amount of people who wanted to garden in urban areas is also rising. Ms. Sullivan says, “In small gardens, on rooftops and indoors, city residents grow fruits, vegetables, grains, and herbs, and raise animals to produce milk, eggs, honey, and meat. City residents use these foods as supplements to food produced by rural agriculture.” Even though some people who live in urban areas grow crops, urban residents still need to rely on food grown in rural areas. This is because a city doesn't have enough space to grow enough food for everyone living in it.

    In New York City, urban farmers have come up with many different ways to grow their own produce, even though there isn't a lot of room. For example, Brooklyn Grange is a farming operation that has two rooftop vegetable farms in New York City. All together, the farms are made up of 2.5 acres of rooftop space. This makes Brooklyn Grange one of the largest rooftop farming operations in the world.

    Brooklyn Grange grows all kinds of things. The farming company sells its vegetables to local residents and restaurants. And because the farms are on rooftops, they are specially adapted to their urban location. They use available space that is not needed for anything else. As more urban farmers find ways to grow food in cities, urban residents will be better able to get fresher materials for their meals.

    In modern society, it is usually considered good to be an extroverted(外向的) person. This means that life can be hard for introverted people. Their talents and abilities are often not recognized.

    Some people often try to make introverts more outgoing. They think that being an introvert is a problem. But there is nothing wrong about being an introvert. Introverts are not necessarily afraid of meeting and talking to others. They simply prefer to spend time on their own, away from the crowds. They like reading, writing and taking walks in the countryside. But extroverts need other people. If they spend a lot of time on their own, they get bored. They tend to be impulsive and talk a lot.

    Our society puts a lot of pressure on people to be extrovert, to be outgoing and self-confident on every occasion. Susan Cain, the author of the book Quiet: The Power of Introverts in a World That Can't Stop Talking, has spoken about this problem. "I was nine years old," Cain says. "In my suitcase there were lots of books. This seemed normal to me, because in our family we always read a lot. I thought it would be the same at summer camp. But I was wrong. To create camp spirit, all the children had to sing a cheer every morning. I couldn't understand why. In the evening, I took out a book from my suitcase. But another girl said, 'why are you being so quiet?' The second time I took out a book, the counselor(辅导员) came to see me. She told me to remember the camp spirit and that it was important to be outgoing."

    At work, extroverts often do well. At job interviews, it is usually good to appear extrovert. It suggests that you will be good at the job. But it is wrong to think that only extroverts are good leaders. Introverts work in different ways to extroverts, but they can still do really great things. Darwin, for example, was a quiet, family man. He often took long walks so that he could think clearly. But Darwin's ideas about evolution were revolutionary.

    Introverts must understand that it is perfectly okay to be the way they are. It is not necessary to want to be the center of attention. You don't have to take part in noisy, social activities if you don't want to. And it is not necessary to try to become more outgoing.

It is certainly difficult to make money. But should money be difficult to give away? In The Gilded Age, industrialists such as Andrew Carnegie and John D. Rockefeller worried about waste and misuse; Carnegie wrote in 1889 that $950 of every $1,000 that went to charity was "unwisely spent". {#blank#}1{#/blank#} Donors ran lengthy application processes, provided funds and fulfilled painstaking reporting requirements. In 2006 The Economist called it "philanthrocapitalism (慈善资本主义)".

{#blank#}2{#/blank#} The 400 richest Americans have given away just 6% of their combined fortunes, according to Forbes. At the last count in 2022, almost $1.2 trn was sitting in American private foundations and $230bn in donor-advised funds, a sort of savings account for donors. Plenty of money is being marked for charity. But it is not getting to worthy causes fast enough.

Fortunately, a new generation of donors is once again shaking up the world of big philanthropy (慈善事业). Leading the mission is MacKenzie Scott, who simplified the process of giving and is donating billions of dollars a year with few conditions. This "no-strings giving" is changing mega-donors' long-held assumptions. {#blank#}3{#/blank#}

One is the recognition that philanthropists do not have to do everything themselves. {#blank#}4{#/blank#} An upside of a decades-long trend for businesslike philanthropy is that armies of consultants have emerged to help donors draw up a strategy and conduct due diligence on potential recipients. Donors can team up and share the work, too.

Another lesson from the no-strings crowd is that philanthropists can trust recipients to put money to good use once the proper due diligence is in place. That means analyzing a nonprofit organization's annual reports and interviewing its leaders and other funders.

A. It offers lessons for those struggling to get money out of the door.

B. In addition to that, her charity work is too numerous to mention.

C. However, this idea that charities' money is wasted has been proven wrong by evidence.

D. Mega-donors no longer need to endure the trouble of setting up a foundation and hiring staff.

E. Two decades on, however, it's become clear that all this paperwork puts the brakes on giving.

F. Around the turn of the millennium donors looked to data and rules as a way to stop waste.