Wind power is a very clean source(来源，出处) of energy. This is how wind power works. Wind makes windmills(风车) spin(旋转). When the windmills spin, they make electricity. Then we can use the electricity.

A lot of people think that wind power is new, but that’s not true. For thousands of years, people have used wind to sail boats and move water. We still do those things today, but these days we mostly use wind power to make electricity.

Wind power is a very popular source of energy. Most people think that we should use it more and more. First of all, it’s clean. Windmills don’t pollute the environment at all. Second, we can use wind power forever. After all, we will always have wind. Also, wind power is cheap, and it’s getting even cheaper.

A lot of people don’t understand wind power very well. They believe that there are problems with wind power, but many of those problems are not real. For example, some people say that windmills are dangerous for birds. They used to be true, but it isn’t true anymore. Old windmills killed birds because they spun very fast. New windmills spin slowly, so they aren’t dangerous for birds.

However, there are real problems with windmills. One problem is that many people think windmills are very ugly. This is a problem for people, because windmills are often in very pretty areas. Also, wind doesn’t blow all the time, so we can’t use wind power all the time. Finally, windmills are noisy.

Although there are several problems, wind power is becoming more and more common. Right now, more than 80 countries use wind power. About 2.5 percent of the world’s power comes from the wind. For some countries, that number is a lot higher. Wind power gives Denmark more than 25 percent of its electricity.

Millions (百万) of years ago, dinosaurs controlled (控制) the earth. And there were different types of dinosaurs on the earth. Some of them were no bigger than chickens, but all of them had very small brains. Later on, there weren’t any dinosaurs. What happened to them?

In the days of dinosaurs, the whole earth was warm and wet. There were many green forests. But the earth changed slowly all the time. When parts of the earth became cold and dry, the forests there died. Then dinosaurs could not find enough food to eat. This must be one reason why dinosaurs died out.

What’s another reason? We can make a guess. New kinds of animals came to the earth. Some had big brains and were fast and strong. They could kill dinosaurs. Some ate dinosaur eggs, too.

There may be other reasons that we do not know about. Each year, people will find some dinosaur footprints (脚印) and bones. Scientists are trying to tell us more about dinosaurs.

As we all know, plants and animals depend on water to live and grow. In fact, water is needed everywhere. Here are some cool facts about water.

Water in our body

Water isn’t just an important part of our planet. It’s an important part of our body, too. More than half of our whole body weight is water. Our body loses water whenever we sweat (流汗) or take a shower. That’s why we need to drink plenty of water every day.

Water in our life

We drink water. We use it to cook, clean, and carry waste out of our homes. Believe it or not, we probably use between about 300 and 380 kilos of water every day.

Water and weather

Water vapor (水蒸气) is the most important gas (气体) around us. It usually stays in the air for less than 2 weeks. It can become the rain which is good for plants. It can also become the snow and children love to play in it. Do you know that the biggest snowflake (雪花) fell in 1887? It was even bigger than a dinner plate (盘子). Is it surprising?

From water to electricity (电)

Water can run very fast. When it rains heavily, its speed through the air may reach at 20 miles an hour. Because of this, people use moving water to make electricity. For example, people built the Baihetan Hydropower Station (白鹤滩水电站) in Sichuan.