B

    When you hear westerners (西方人) say "Drop in anytime(随时来玩)"  or "Come and see me soon", you should realize that it doesn't mean you are welcome to come over to their house anytime. It's wise to telephone before visiting someone.

    Never accept an invitation unless (除非) you really plan to go. You may refuse (拒绝) by saying, "Thank you for inviting me, but I may not be able to come." If you are unable to come after accepting the invitation, be sure to tell those who invite you in advance (提前) that you will not be there.

    When you have accepted the invitation to a party or a dinner, it is polite to bring small gifts with you, such as bottles of drink, flowers and some others. Sometimes westerners may take you out to dinner in a restaurant and it does not necessarily mean that he is going to pay the bill at the end of the meal. He might want you to "go Dutch", which means each person pays his own bill.

    Sometimes people cry when they are sad. Other times people cry tears of joy. But your eyes make tears all the time, whether you are crying or not. Do you know the tears help keep your eyes healthy? They keep your eyes from drying out. A special area of the eye drips (滴) all the time. It keeps the eye humid.

    If you look in a mirror, you can see tiny holes in the comers of your eyes. Each hole leads to a small tube that runs to your nose. Tears run slowly into this tube drip by drip. Day and night the holes drain (流走) the tears away. If they didn't, you would always look as if you were crying.

    If you begin to cry, there are many more tears. The holes can't drain all of them. Then extra tears run out onto your face.    

    Tears help keep eyes safe. If there is something harmful in the air, the eyes fill with tears. These tears coat your eyes. They keep the harmful air out.

    Contact lenses(隐形眼镜) can make the eyes too dry. Some people have to add tears to their eyes. They buy bottles of eye drops to keep their eyes wet.

Are You Right Handed or Left Handed?

    Which hand do you use when write? About 8 to 15 percent of people are left handed. They often have to use tools that are designed for right-handed people. So it is difficult for left-handers to use most tools. If you are right handed, try this experiment: Take a knife with your left hand and try cutting a potato into pieces. Don't be surprised if you feel awkward（别扭的）.

    In the past, people thought it was strange to use the left hand. Young students looked down upon their left-handed classmates. Some children were even punished for using their left hand to write. But these days parents and teachers have accepted that. In almost every school in the world, left-handed students can use their left hand to write.

    What causes people to be left handed or right handed? Experts have searched long and hard on this. They concluded（得出结论） that left-handed people are left handed for the same reason that right-handed people are right handed. One out of every ten people just is a left-hander. It's simply like the color of our eyes—some people have brown eyes, while some others have black eyes.

    However, many researchers think that left-handers and right-handers are different in some aspects. Right-handers are more talkative and outgoing than left-handers. Many right-handed people understand spoken words better. For example, after they listen to directions to a supermarket, they can find it easily. Right-handers are good at organizing people, too. They are also better basketball guards. Just ask Yao Ming.

    Research shows that left-handers are creative and artistic. Many famous performers, like Jim Carrey and Paul McCartney, are left handed. Many left-handers learn better visually（在视觉方面）. In art, both Leonardo da Vinci and Michelangelo were left handed. In science, you find Newton and Einstein. The left-handed people are also really good at tennis and other single sports.

    If you prefer one hand, but you are still good at writing with the other, you are mixed handed. Research shows mixed-handers can remember everyday things better than other people. What did you eat for lunch two weeks ago? If you're mixed handed, you can probably remember.

    Thousands of years ago, people didn't know that the Earth moved. They thought the sun really did move across the sky. The Greek god Helios was said to drive the sun across the sky with his chariot (战车). But now, the way people think has changed. Nowadays, it is the sun that drives a "chariot" around the sky.

    What do I mean by this? Well, quite simply, there is now a plane (or "chariot") that is powered by the sun. It has special parts on its wings. These parts absorb (吸收) power from the sun. They absorb so much power that the plane can still fly even at night. In Greek mythology (神话), Helios had to take a break at night. It seems we're finally even more powerful than the gods themselves.

    This plane is called Solar Impulse. It will fly across the US in May. This is very important for the future of the world.

    Why is solar energy (太阳能) important? Well, other kinds of energy are known to cause problems. If you live in China, you've probably noticed the pollution. This is caused by burning coal and gas to make energy. The heat and chemicals created by burning these things give us power. But if we use power from the sun, we don't have to burn anything and there will not be any pollution.

    Solar energy is not entirely ready yet. It needs to be improved. But the best thing about it is that, unlike coal and gas, it doesn't run out. The Solar Impulse plane could pretty much keep flying forever. Of course, the sun's light will eventually run out too one day, but not for another 5 billion years. That's a pretty long flight.