The world 1 many interesting sounds. Some are unpleasant to our ears while 2 are very pleasant to hear. In single day you probably hear 3 sounds. All sounds are different. Some 4 loud, some sounds are high, others are low, some sounds are useful.

    5 sound we can't talk or listen to each other. The ringing of the alarm clock wakes people up. The hooting（鸣笛声）of a car warns people of danger.

    Some sounds are harmful. When planes fly low 6 the land; the very loud sounds can damage the house. Very loud sound can even make people deaf.

    We know sound travels about one kilometer in three 7. In a thunder（雷）storm you see the lighting first and then hear the thunder. This is because light travels 8 than sound.

    Next time you see lighting count the number of seconds before you hear the thunder.

    Divide（分成）this number 9 3. This will tell you 10 kilometers away the thunder storm is.

    The computer is fast, and never makes a mistake, while people are too 1 and full of mistakes sometimes. That's what people often say when they talk about computers. For over a quarter of a century, scientists have been 2 better and better computers. Now a computer can do a lot of everyday 3 wonderfully. It is 4 used in factories, hospitals, post offices and airports. A computer can report, decide and control in almost every field. Many computer scientists are thinking of making the computer “think” like a man. With the 5 of a person, a computer can draw pictures, write music, talk with people, 6 chess, recognize voices, translate languages and so on. Perhaps computers will one day really think and feel. Do you think the people will be 7 when they find that the computer is too clever to listen to and serve the people? No, people will make 8 use of the computers in the future. Man is always the master of the computer. The computer 9 only with the help of man. It cannot take the 10 of man.

Empathy(同情心) lets us feel another person's pain and drives us to help. Do any other animals feel empathy? Scientists recently found that rats(老鼠) do, too.

    Most people don't like rats. In many people's eyes, rats are only bad. But Jean Decety and his partners at the University of Chicago did an experiment. It showed that rats are kind, warm-hearted animals. They can feel each other's pain.

Scientists placed pairs of rats in plastic cages(笼子) for two weeks. During this time they got to know each other. Then they put one of the rats from each pair into a small container(容器) in the cages. The small container had a door. It was so designed as to fall to the side when the free rat touched it. Many of the trapped(困住的) rats squeaked(吱吱叫) to show their discomfort. The other rats of the pairs could see their suffering friends clearly.

In most pairs, the free rats would become very worried about their friends. They kept trying to save their friends again and again throughout the month. Scientists put the rats' favorite chocolate in the cages, but the rats didn't eat it until they had saved their friends successfully. Scientists also found that female rats seemed to act more empathetic than male rats.

    “The results are the first to show that rats take action in response to another's trouble,” Decety said. “Monkeys and chimpanzees have similar behavior. But unlike those animals, rats can be ready used in laboratory studies. They will help us to learn which parts of the brain lead to empathy and helping behavior and whether empathy is natural.”

    Every year some people are killed or injured in road accidents.There are rules to 1the roads safe, but 2people do not always obey(遵守)the rules.They are 3.If everybody obeys the rules,the roads will be 4.How can we make the roads safe?Remember this rule:traffic must keep to the right.Cars,buses and bikes must 5keep to the right side of the road.Before 6the road,stop and look 7.

    Then,if you are sure that 8is clear,it is safe to cross the road.If you see small children, very old people,or blind people waiting to cross the road,it is 9to help them cross the road safely.

    We must teach children to cross the road safely.We must tell them 10on the street.We must always give them a good example.

    We are lucky to live in a rich country where we have many things. However, some of us sometimes 1 some things.

    Electricity is one thing that we waste most. Lights, TVs, radios and other things are often kept on. We should turn them off when no one is using them. It 2 less than a second to do it. Anyhow, not wasting electricity 3 money, because we do not have to pay for the electricity we do not use.

    The second thing that we often waste is water. 4 water is precious (珍贵的) and important, so it shouldn't be wasted. It is only a(n) 5 matter of turning off a tap. I am sure everybody can do it 6 if he wants to.

    Another big waste is 7. My mother used to cook so much food that much of it was thrown away. I told her we had wasted so much food. She thought l was 8. And now she cooks only what we can 9 up.

    It is not right to be wasteful. I find there is a simple way of not wasting things. That is to use only what we need and not to 10 what we do not need. In this way, we can stop being wasteful.