If you want to use water for electric power and to prevent flooding or drought, what should you do? 如果你想用水发电，防洪或防旱，你该怎么做？

　　You have to make a dam. 你得建座水坝。

　　A dam is very useful for many reasons. 水坝非常有用的原因有很多。

　　A long time ago, people build dams to grow grains and vegetables. 很久以前，人们筑水坝来种粮食和蔬菜。

　　What was the first dam in history? 历史上第一座水坝是哪个？

　　It was a dam in Jordan. 它是约旦的一座水坝。

　　But the dam was soon destroyed by rain. 但它很快就被雨水给冲毁了。

　　Now, there are millions of dams all over the world. 现在，全世界有几百万座水坝。

　　Without dams many cities will be flooded every time it rains. 没有了水坝，每次下雨很多城市都会被水淹没。