Stress is the feeling you get when you're really worried about something. This is the kind of worry that troubles you for hours, or 1 days. It makes you feel blue, scared or angry. You may find it 2 to eat and sleep, or you might eat and sleep much more than usual.
Too much stress is bad for you. Stressing out can lead to serious 3 like heart illnesses. But a moderate (适度的) amount of stress keeps your body and 4 alert (警觉的) and can make your performance better, like when you are doing a presentation to your class or 5 to the finishing line.
    But, if you are seriously stressed out, look at these quick and easy ways to 6. Firstly, you can go for a run, play tennis or ride your bike for a while 7  exercise produces more beta-endorphin(B-内腓) that controls stress. Secondly, having a good 8 is very important. You should try to get at least eight hours of sleep every night. Thirdly, eating a healthy, balanced diet that 9 all the food groups will help. Also, you can talk to the people you trust . Keeping your feelings inside may make the situation10 while talking to a person you trust may make you feel better. They may be able to give you advice and help you solve your problem.

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.”

    People like dolphins because they are both lovely and clever. They have an 1 IQ (智商).

Dolphins can 'talk'. Scientists try to ‘talk' with dolphins, and the results make them 2. They find that dolphins 3 understand them so well.

4 animals enjoy playing, but dolphins like to make their games different. On a beautiful day in 1997, scientists on a beach 5 a little dog going into the sea. They were surprised to see the dolphins come up to the dog and then start throwing(扔) it into the air. The dog 6 the 'game' and kept playing with the dolphins for over an hour.

    Dolphins live in a very different world from 7, but they are very good at our 'IQ tests(测试)'. For example, in the picture above, a dolphin jumps 8 the water when he hears a whistle noise(哨声). He does this because he will get a fish 9 an award.

    There is 10 much to learn about these lovely friends.

    Light travels at a very fast speed. It is about a million times1than the speed of sound. You can get some idea of this2by watching the start of a race. If you stand some distance away from the starter, you can see smoke from his gun before the sound gets to your 3.

    This great speed of light4some strange facts. Sunlight5about 8 minutes to get to us. If you look at the light of the moon tonight, 6 that the light rays(光线)leave the moon 1.3 seconds before they get to you. The nearest star is so7away that the light which you can see from it tonight started to8towards you several years ago. In some cases, the light from one of tonight's stars had started on its journey to you before you were born.

    So, to be exact, we can't say, "The stars are shining 9."We have to say instead, "The stars10pretty. They were shining several years ago, but their light has only just got to the Earth."