Napoga is a 12-year-old girl in Ghana(加纳), Africa. It is hard for her family to get clean water. Every morning, she leaves home at half past five to get clean water for her family in a village far away. It takes her six hours to get enough clean water for daily(日常) cooking and drinking. She has no time to go to school or to play with her friends. Millions of people in the world are like Napoga. They can't get enough clean water to keep healthy.

    Earth Day is on April 22. But on all other days, we must also remember it. The water we use is the most important natural resource(自然资源) on the earth.

    Water covers 70% of the earth's surface(表面). But most of that is sea water. We can't use it for very many things. Fresh water covers only 1% of the earth's surface.

    You probably feel lucky that your life isn't as hard as Napoga's. But that doesn't mean you don't have to worry about water. We all face serious water problems. One of them is water pollution. All kinds of things from cars, factories, farms and homes make our rivers, lakes, and oceans dirty. Polluted water is very bad for people to drink. And dirty water is bad for fish, too. Now, 34% of all kinds of fish are dying out.

    How do cars and factories make our water dirty? First, they pollute the air. Then, when it rains, the rain water comes down and makes our drinking water dirty. Dirty rain, called acid rain(酸雨), is also bad for plants, animals and buildings.

    Scientists say that in 30 years, more than half of the people in the world won't have enough clean water. We have to learn how to save more water for ourselves and our children. Here is some advice for saving water:

●Turn off the water while you brush your teeth. You can save as much as 450 liters(升) each month.

●Leaky taps(漏水的龙头) waste a lot of water. Fix them right away!

●You can easily cut your 10-minute showers(沐浴) in half—and you'll be just as clean.

●When you wash dishes, don't let the water run.

●Only wash clothes when you have a lot to wash. If your washing machine isn't full, you're wasting water!

    Light and shadow（影子）are friends. They usually go together. We receive light every day. At the same time, we produce shadow.

    Light cannot shine through you. Your body stops it from passing. There is a dark spot on the ground next to you. The light cannot reach the dark spot. This is your shadow.

    At noon the Sun shines over your head. Your body stops very little light from reaching the ground.

    We love light, especially sunlight. Without sunlight, life on the Earth is impossible. Most of us like to stand in the shadow of a tree in summer. But some people are afraid of their own shadow at night. They do not want to walk in a dark street. They do not want to see the shadow either. But still light and shadow usually go together.

    Imagine one day, the water taps (水龙头) in your house stop running. You have to buy water from shops. And still there isn't enough for everyone. Your mother has to save the family's shower water to do other things. Would you be able to stand that kind of life?

    Probably not. But that's what kids in Yemen are experiencing. Experts said Yemen is going to be the first country in the world to run out of water. According to a report, the capital, Sana, will run out of drinking water as early as 2025.

    Because of the shortage, the government often cuts the water supply(供应). Hannan, an 18-year-old from Lahej, told Times, "In a good week we'll have a water supply all week. But then the following week there will be water only for a day or two."

    Hannan said only rich people have enough water to use. They can buy water from the shops or from the water trucks. Private companies own the trucks. They travel around the city every day to sell water—at very high prices. "A lot of people can't afford it," she said.

    The average(平均) person in Yemen uses 100 to 200 cubic(立方) meters of water per year. That is far below the international water poverty(贫困) line of 1,000 cubic meters.

    The government is thinking of making use of seawater. But it will cost a lot and it may not happen soon enough to help the people of Yemen.

    There are many colours in nature. But do you know if a colour has weight? I think you'll say "no". But I am afraid you are wrong. If you don't believe, you may do a small experiment.

    First, put two objects with the same weight into two boxes. Then, cover the box. Third, wrap(包裹) one box with a red piece of paper, the other with a white piece of paper. OK. Now hold the boxes with your hand one by one. It is certain that you will think the red one is a little heavier. Why do you think so? A scientist found that different colours have different weight in a man's mind. So he did many tests and at last he got the result. That is to say, every colour has its own weight in our mind and their order(顺序) is the same. The heaviest colour is red, then blue, green, orange, yellow and white.

    The scientist told us that colours also have smell. Can you smell the colour? Of course not. Then why did the scientist say so? That is because every colour stands for a kind of light with a certain wavelength (波长). It reaches our brain(大脑) through sense organs(感觉器官).

    According to this discovery, scientists say that people accept the colours they like, and refuse the colours they hate. So your body and mind will be healthy by using the colors you like. Or you'll be nervous or even get ill. For example, if you stay in a room with red windows, wallpapers and furniture for two hours, you'll feel you have been there for four hours. But if the room is blue, you'll feel you have been there for only an hour. Another example, if a person walks out of a red room and into a blue room, his temperature will fall. That means our body temperature will change with different colours.