【正确答案】The Earth
   The earth is now the only planet that is fit for human beings. The air around it forms a protection that prevents the earth from getting neither too hot nor too cold. The water, the trees, and other things on the earth are essential for man.
   Unfortunately, the earth we live on is severely damaged because of the high civilization. Modern factories provide us with best commodities at the cost of polluting the environment. To meet the needs of the ever-increasing population, we are using up natural resources.
   Measures must be taken to protect the earth. First, we should teach people the importance of the environmental protection. Second, we should make machines that will use less energy and will do the minimum damage to the environment. Third, we must figure out ways to make use of waste to save natural resources.