In the past hundred years, there have been frequent natural disasters, ______ as floods, droughts, earthquakes. The disasters have killed m______ of people, destroyed countless homes, and wiped out numerous ______ (piece) of land. Now more and more people become a______ that those disasters have much to do ______ what we have done to the earth. We have cut down many trees in the forests, and have badly ______ (pollute) the environment. As a ______, climates have become worse and worse. The earth is our home-planet. It’s urgent for us to stop ______ (damage) it, and to do our best to p______ it and make it a lovely place suitable to live in, for we have n______ to go and survive except where we are now.