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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    It is hardly surprising that clothing manufacturers (生产商) follow certain uniform standards for various features (特征) of clothes. What seems strange, however, is that the standard adopted for women is the opposite of the one for men. Take a look at the way your clothes button. Men's clothes tend to button from the right, and women's from the left. Considering most of the world's population—men and women—are right-handed, the men's standard would appear to make more sense for women. So why do women's clothes button from the left?

    History really seems to matter here. Buttons first appeared only on the clothes of the rich in the 17th century, when rich women were dressed by servants. For the mostly right-handed servants, having women's shirts button from the left would be easier. On the other hand, having men's shirts button from the right made sense, too. Most men dressed themselves, and a sword drawn from the left with the right hand would be less likely to get caught in the shirt.

    Today women are seldom dressed by servants, but buttoning from the left is still the standard f0r them. Is it interesting? Actually, a standard, once set, resists change. At a time when all Women's shirts buttoned from the left, it would have been risky for any single manufacturer to offer women's shirts that buttoned from the right. After all, women had grown so used to shirts which buttoned from the left and would have to develop new habits and skills to switch. Besides, some women might have found it socially awkward to appear in public wearing shirts that buttoned from the right, since anyone who noticed that would believe they were wearing men's shirts.

    From the health point of view we are living in a wonderful age. A large number of once fatal illnesses can now be cured by modern drugs and surgery. But though the possibility of living a long and happy life is greater than ever before, every day we witness the unbelievable killing of people on the roads. Man is opposite to the motor-car! It is a never-ending battle which man is losing. Thousands of people are killed each year and we are quietly sitting back and letting it happen.

    It has been rightly said that when a man is sitting behind a steering-wheel(方向盘), his car becomes the extension of his personality. There is no doubt that the motor-car often brings out a man's worst character. People who are normally quiet and pleasant may become unrecognizable when they are behind a steering-wheel. They are rude, ill-mannered and aggressive. All their hidden frustrations and disappointments seem to be brought to the surface by the act of driving.

    The surprising thing is that society smiles on the motorist and seems to forgive the behavior. Everything is done for his convenience. Cities and towns are made ugly by huge car parks.

    It is high time a world law were created to reduce this senseless waste of human life. With regard to driving, the laws of some countries are not strict and even the strictest are not strict enough. A law which was universally accepted could only have a beneficial effect on the accident rate. Here are a few examples of some things that might be done. The driving test should be made to a fixed standard and far more difficult than it is; all the drivers should be made to take a test every three years or so; the age at which young people are allowed to drive any vehicle should be raised to at least 21; all vehicles should be put through strict annual tests for safety. Present drinking and driving laws (where they exist) should be made much stricter. Driving speed should be limited on all roads. These measures may sound rather severe. But surely nothing should be considered difficult if it results in reducing the annual toll of human life. After all, the world is for human beings, not motor-cars.

    I started reading Shakespeare when I was nine, after my grandfather, an actor, sent me a copy of Romeo and Juliet. The story and the language attracted me. I found out about Shakespeare Globe Centre New Zealand (SGCNZ) and started volunteering for them when I was about 10. When I was 13, I managed to run a film project with SGCNZ.

    I'm home-educated and a part-time correspondence student (函授生) as well. We have a drama group made up of quite a few people who are also home-educated .I've also joined Wellington Young Actors, a youth theatre company. There are many similarities and differences between being home-educated and attending a five-day programme. I love hearing other students' reactions when meeting them and share my different ways of experiencing the world with them. While explaining the way I learn can be a challenge, I love helping people to understand there isn't just one way of learning.

    Being home-educated has offered me the freedom to have an individualized education and to pursue my passions. My education has always been about making those focuses but I do lots of the same things as people who attend five-day programs do. Shakespeare is a great approach to lots of things around English, history and the arts. I think something you learn when you perform is connection. You have to have a connection with your fellow actors, with the audience and with Shakespeare. I learn this from actually being on stage and from taking part in different Shakespeare festival programs.

    I believe it's the emotion in Shakespeare that makes it relevant today. You can be reading something that was written 400 years ago and be able to see parts of your life in the work as it shows you how to understand the world and explore a lot of different ideas.

I was a lecturer for 10 years when I met my greatest teacher. It wasn't in a 1 but in a hospital. She was my daughter Kelsey.

She was born with congenital cerebral palsy（先天性脑瘫). At four, she still 2 to tie her shoes. It was 3 for her. After three years of 4 , Kelsey made it. Her accomplishment taught me that pace wasn't going to be crucial—achieving goals according to her own 5matters most.

At age 5, she won a battle against cancer. Kelsey 6 through creative play. In the hospital, the game was always "restaurant" with her playing waitress and the rest of us 7 as customers. She enjoyed herself in the 8 for several hours 9 , as if we weren't in the hospital at all. At home, the play turned to "hospital." Her game included medical terms even we adults didn't understand. We'd just play along as she 10 herself in her roles.

At six, she wished to take ballet lessons. I'm embarrassed to admit how much this 11 me. I wasn't just afraid for her body, but for her 12 .

I worried about the 13 she might get from the class. But she wouldn't 14 and the expectation in her eyes 15 all the drawbacks, so we enrolled her in a ballet school.

Kelsey danced with 16 ! Did she fall? Of course. Was she awkward? Very. But she was completely 17 by her situation. The sheer joy of dancing was enough. After four years, she 18 to horse riding. This time, I signed her up without 19 .

Now a seventh grader, Kelsey continues to embrace her life and teach us invaluable 20 about persistence and the power we could never have otherwise.

Kelsey, I'll never have a greater teacher!

The periodic table of elements is a common sight in classrooms，campus hallways and libraries. The mode periodic table arranges the elements by their atomic numbers and periodic properties（周期性）. Several scientists worked over a century to assemble the elements into this format. 

In 1789，French chemist Antoine Lavoisiertried grouping the elements as metals and nonmetals. Forty years later，German physicist Johann Wolfgang Dobereiner observed similarities in physical and chemical properties of certain elements. He arranged them in groups of three in increasing order of atomic weight and called them triads，observing that some properties of the middle element，such as atomic weight and density，approximated the average value of these properties in the other two in each triad. 

A breakthrough came with the pu blication of a revised list of elements and their atomic masses at the first international conference of chemistry in Karlsruhe，Germany，in 1860. They concluded hydrogen would be assigned the atomic weight of 1 and that the atomic weight of other elements would be decided by comparison with hydrogen. For example，carbon，being 12 times heavier than hydrogen，would have an atomic weight of 12. 

In 1869，Russian chemist Dmitri Mendeleev created the framework that became the moder periodic table，leaving gaps for elements that were yet to be discovered. Mendeleev predicted the properties of some undiscovered elements and gave them names such as"eka-aluminum"for an element with properties similar to aluminum. Later "eka-aluminum"was discovered as gallium. 

German chemist Lothar Meyer produced a version of the periodic table similar to Mendeleev's in 1870. He left gaps for undiscovered elements but never predicted their properties. The Royal Society of London awarded the Davy Medal in 1882 to both Mendeleev and Meyer. The later discovery of elements predicted by Mendeleev verified（证实）his predictions and his periodic table won universal recognition. In 1955 the 101st element was named mendelevium in his honor. 

On UNESCO website，it wrote，"The Periodic Table of Chemical Elements is more than just a guide or catalogue of the entire known atoms in the universe；it is essentially a window on the universe，helping to expand our understanding of the world around us. "