some people imagine to leave this fearful world, only to come down to earth. scientists tell us that of all the stars known in the vast universe, the earth is the only planet on which human beings can survive. but now we are facing the risky problems concerning our existence on earth.

　　worldwide environmental deterioration is alarming. the earth is plagued with population explosion, energy crisis, lack of food, housing problem and environmental pollution. during the process of industrialization, human beings are pursuing crazily the benefits from the economic growth. now we have suffered from the results. the overuse of natural resources has affected ecosystem on earth.

　　environmental deterioration has critically upset the balance of nature. the damage mainly attributes to man`s ignorance, greed and wastefulness. for immediate interests human beings have overused earth resources with no thought for the future. now the terrible damage poses a severe challenge to our existenceg then what will our future be if we do not act now ⅱ