If you answer "Yes" to more than two of these questions, you are one of those people with stress. So what can you do about it?
Doing relaxing exercises, talking with friends and listening to light music are all usual ways of relieving（减轻） stress. However, doctors now say that there are easier ways—people should laugh and smile more often. When you laugh and smile, your body relaxes. They also say that people, especially men, should cry more often, be­cause crying is the natural way of relieving stress.

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    Have you ever wondered how and why a fall leaf changes color? We first have to understand what leaves are and what they do.

    Plants are the world's food factories. Plants take water from the ground and take CO₂ from the air. Plants use sunlight to turn water and CO₂ into glucose(葡萄糖). Glucose is a kind of sugar. Using it as food, plants get energy and grow. Plants using sunlight to turn water and CO₂ into sugar is called photosynthesis(光合作用). ChlorophyII helps photosynthesis. It gives plants their green color.

    As summer ends and autumn comes, the days get shorter and shorter, and trees "know" to begin getting ready for winter. During winter, there is not enough light or water for photosynthesis. Trees rest during this time and live on the food they store during the summer. They begin to shut down their food — making factories. As the green chlorophyII disappears from the leaves, we begin to see yellow and orange leaves. These colors have been in the leaves all the time. We just can't see them in the summer, because they are covered up by the green chlorophyII.

    The bright reds and purples we see in leaves are made mostly in autumn. In some trees, glucose is caught in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn turn this glucose into a red color. The brown color of trees is made from waste left in the leaves. It is mixture(混合物) of all these things. It makes the beautiful leaves during autumn.

    We know the mosquito very well. Mosquitoes fly everywhere. They can be found almost all over the world, and there are more, than 2, 500 kinds of them.

No one likes the mosquito. But the mosquito may decide that she loves you. She? Yes, she. It's true that male mosquito doesn't bite and only the female mosquito bites because she needs blood to lay eggs. She is always looking for things or people she wants to bite. If she likes what she finds, she bites. But if she doesn't like your blood, she will turn to someone else for more delicious blood. Next time a mosquito bites you, just remember you are chosen. You're different from the others!

    If the mosquito likes you, she lands on your body without letting you know. She bites you so quickly and quietly that you may not feel anything different. After she bites, you will have an itch(痒) on your body because she puts something from her mouth together with your blood. By the time the itching begins, and she has flown away.

And then what happens? Well, after her delicious dinner, the mosquito feels tired. She just wants to find a place to have a good rest. There, on a leaf or a wall, she begins to lay eggs, hundreds of eggs.

    The earth is about 4,600 million years old. Modern man has lived on the earth for only 35,000 years, but during that time, we have changed our planet in many ways. Many of the things that we have done are good, but more are not good for the earth.

    Water pollution

    A lot of people, birds and fish die each day because of water pollution. Factories have polluted the land and the water. As a result, many river and lakes are now dead.

    Air pollution

    In big cities, factories, as well as cars, trucks and buses are the biggest cause of air pollution. Many people in cities now have bad health problems. For example, Mexico city used to be a beautiful sunny capital, but today it is almost covered by thick brown clouds.

    Soil pollution

    In order to have a good harvest, most of the farmers use chemicals too much on their fields. That's bad for the soil. But this kind of pollution is difficult to stop.

    Hope for the future

    These problems are very serious for our future, so all of us should do something to improve our environment. If we can stop pollution, our planet will become more and more beautiful and our health will be better. Let's be greener people.

    China Science and Technology Museum was opened to the public in September 1988. But the second project was completed in May, 2000. Its main task is to spread knowledge of science and technology among the public.

    The activities of China Science and Technology Museum include popular science exhibitions, Astro­vision film shows, training education programmes and experiment exhibition programmes. The museum has an area of 40，000 square metres, of which 16, 000 square metres is for exhibition halls.

    The Astro­vision Theatre is one of the museum's major attractions and also one of the largest Astro­vision theatres in the world. It makes visitors feel they are in actual events rather than see a film. Many great science activities are often held at the museum, and the museum wants to be an important window to the world.

    Each year more than2,500 people die and 12,600 are injured in home fires just in the UnitedStates, with direct property(财产) lossbecause of home fires at about $7.3 billion every year. Every day Americansexperience tile horror(惨状) of fires, but most people don'tunderstand fires.

    To protect yourself, itis important to learn something about home fires.

    In less than 30 secondsa small flame can get completely out of control and turn into a major fire. Itonly takes minutes for thick black smoke to fill a house or for it to be inflames. Most deadly fires occur in the home when people are asleep, lf yourealize a fire, you won't have time to take valuables because the fire spreadstoo quickly and the smoke is too thick. The fire uses up the oxygen you needand produces smoke and poisonous(有毒的) gases that kill. Breathing even small amounts of smoke and toxicgases can make you tired and sleepy, and short of breath. The smoke can causeyou to be a deep sleeper before the flames reach your door. You may not wake upin time to escape.

    Room temperatures in afire can be 100 degrees at floor level and rise to 600 degrees at eye level.Breathing in this super-hot air will burn your lungs. It can melt clothes toyour skin. In five minutes, a mom can get so hot that everything in it startsto burn at once.

    Fires are bright atfirst, but quickly produce black smoke and complete darkness. If you wake up toa fire you may be blinded, confused about where you are or which direction you shouldgo in and unable to find your way around the home you've lived in for years.

    Only when we know thetrue nature of fires can we prepare our families and ourselves.