阅读下面一篇短文，根据其内容填空。

Wind power is a very clean source of energy. This is how wind power works. Wind makes windmills 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. Wind mills 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. That used to be true, but it isn’t true anymore. Old windmills killed birds because they spun very fast. New windmills spin slowly, and 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 some 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.

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.

（1）Wind power can be turned into __________ when windmills spin.

（2）People have used wind to __________ and move water for a long time.

（3）New windmills don’t __________ because they spin at a slow speed.

（4）One of the real problems with windmills is that they __________.

（5）This passage mainly introduces a kind of clean, __________ energy to us.