In the past hundred years, there have heen frequent natural disasters, such as floods, droughts, mud-rock flows, seismic sea waves, earthquakes, windstorms and the stretching of new deserts. The disasters have killed millions upon millions of people, destroyed countless homes, and wiped out numerous pieces of fertile land.

Now more and more people become aware that those disasters have much to do with what we have done to the earth. We have cut down too many trees in the forests,we have badly polluted the environment, we have shocked our own home-planet time and again with tremendously powerful explosions of nuclear bombs. As a result, climates have become abnormal, rainwater rushes down hillsides angrily, and the underground energy goes up to revenge itself on us.