We've talked about snails (蜗牛) and their slow move . But much of the time snails don't move at all. They're in their shells (壳)—sleeping .

    Hot sun will dry out a snail's body. So at the least sign of hot sun, a snail draws its body into its shell and closes the opening with a thin cover .Then it goes to sleep. A snail will die in a heavy rain. So whenever it rains, it goes inside its shell house and goes to sleep. A snail can sleep for as long as it needs to. It can take a short sleep. Or it can sleep for days at a time .And it spends all the winter months in its shell, asleep.

    In spring the snail wakes up .Its body, about three inches long, comes out of from the shell. When hungry, the snail looks for food. It can't see very well. Its eyes ,at the ends of the top feelers (触角)are very weak . But its sense of smell is very strong. It helps the snail to the new greens. Then the snail's little mouth goes to work.

    A snail's mouth is no longer than the point of a pin(针) . Yet it has 256,000 teeth! The teeth are so small that you can't see them. But they do their work. If you put a snail in a hard paper box, it will eat its way out. And if a snail wears out its teeth, it will grow new ones.

    Mostly, a snail looks for food at night .But on cloudy days it eats in the daytime. It eats all day long. A snail can go on eating for hours and never feel full.

    North American black bears are shy animals. They are fearful by nature, and will usually run away if they see or hear people. Because of this, it can be difficult for scientists to learn about these animals.

    In order to study black bears, researchers from New Jersey, the US, catch bears and use drugs to help them go to sleep. Researchers then work out the size and the weight of the bears, take blood, to test for diseases, remove a tooth and take it to the lab to find out its age. From these studies, researchers want to find out how many bears live in New Jersey, how long they live, and how many babies they produce.

    But in Minnesota, the US, researchers study bears that are completely awake. The bears know the researchers' voices and they are not afraid of the research team. With the help of a few grapes to keep the bears busy, researchers can touch them to check their hearts, look at their teeth, and do other jobs. Researchers can also walk or sit with bears for hours and make videos to learn about their everyday lives."

    In both places, the main purpose is the same—to make sure there is a healthy population of black bears. But the research methods and the kinds of information that researchers are able to collect are quite different.

    A hundred years ago, most people thought that human beings would never fly. And the idea of flying seemed crazy and dangerous. But as a new world full of new inventions（发明物）came, everyone was trying to break the old thoughts. So many inventors, like Orville and Wilbur Wright, tried to make a flying thing.

    Most plane inventors at that time were impulsive. They would think of an idea, make a plane as quickly as they could, and then try to fly it as soon as possible. All of them had the same result they took their planes home and they had no idea why they didn't work.

    However, the Wright brothers were much smarter inventors. They tested their ideas in smaller or safer ones before making a real plane. For example, the Wright brothers made a wind tunnel(隧道)to compare(比较)wing shape ideas. They also flew lots of kites to test their ideas. They studied the way birds fly through the air and tried to learn something from it when making their models. Finally, the Wright brothers felt they were ready to test their planes, but they needed to find the right place. They knew the right place to test their planes after writing to the US Weather Bureau for help. At last on December 17th, 1903, Orville and Wilbur tested the plane and they made it.

    The plane flied for twelve seconds and it traveled just 120 feet, but Orville and Wilbur were very happy. Their plane really worked! By the end of the day, both brothers had great successful flights(飞行), with Wilbur having a record of 852 feet in 59 seconds.

    In most parts of the world, many students help their schools make less pollution. They join "environment clubs". In an environment club, people work together to make our environment clean.

    ●No-garbage lunches. How much do you throw away after lunch? Environment clubs ask students to bring their lunches in bags that can be used again. Every week they will choose the classes that make the least garbage and report them to the whole school!

    ●No-car day. On the no-car day, nobody comes to school by car—not the students or not the teachers! Cars give pollution to the air, so remember:

    Walk, jump, bike or run.

    Use your legs! It's lots of fun!

    ●Turn off the water! Did you know that some toilets can waste twenty to forty liters (升) of water an hour? In a year that would fill a small river! In environment clubs, students mend those broken toilets.

    We love our environment. Let's work together to make it clean.

    In the universe, as we know, there is the Sun, the moon, the Earth and a good many stars. Through our geography lessons, we know the Earth goes around the Sun, and the moon goes around the Earth. We have day and night because the Earth keeps turning all the time. When our part of the Earth turns to the Sun, it is day. When our part of the Earth turns away from the Sun, it is night.

    Just because the moon is closer to the Earth than the Sun, it looks much bigger than the Sun. Big things will look smaller when they are farther, and small things also look bigger when they are nearer.

    The Sun is bright enough to give out very strong light. The moon can't give any light at all, but it looks quite bright, too. Why？In fact, the light from the moon comes from the Sun. The moon looks much bigger and brighter than the stars. But actually (事实上) the stars are much bigger and brighter than the moon. They look smaller than the moon also because they are farther away from the Earth.

    There are still many other planets in the universe. But of all these planets, only on Earth there are living things and people can only live on Earth, too. But at 9∶00 am on October 15th 2003,Chinese astronaut Yang Liwei was set up to space. He stayed there for 21 hours. It was the first time for Chinese to get into space.

    Different weather makes people feel different. It influences(影响) health, intelligence(智力) and feeling.

    In August, it is very hot and wet in the southern part of the United states. People there have heart trouble and other kind of health problems during this month. In the northeast and the Middle West, it is very hot at some times and very cold at other times. People in these states have more heart trouble after the weather changes in February or March.

    The weather can also influence intelligence. For example, in a 1983 report by scientists, IQ of a group of students was very high when a very strong wind came, but after the strong wind, their IQ was 10% lower. The wind can help people have more intelligence. Very hot weather, on the other hand, can make it lower. Students in many schools of the United States often get worse on exams in the hot months of the year(July and August).

Weather also has a strong influence on people's feelings. Winter may be a bad time for thin people. They usually feel cold during these months. They might feel unhappy during cold weather. But fat people may have a hard time in hot summer. At about 18℃, people become stronger.

Low air pressure(气压)may make people forgetful, People leave more bags on buses and in shops on low－pressure days. People feel best at a temperature of about 18℃. Are you feeling sad, tired, forgetful or happy today? It may be the weather's problem.