【答案解析】
Man is part of nature. They can only survive if they live in harmony with nature. Otherwise the ecological balance will be broken and man has to pay for what he has done to his environment.
In its narrow sense, nature here refers to the natural environment around us including plants and animals. Trees can clean the air by absorbing harmful gases like carbon dioxide. Forests can maintain a good and stable climate, provide habitat for wild lives, and prevent sandy wind from passing people. Almost all the green plants can serve as specialists in beautifying nature and purifying air.
Animals are good friends for mankind. Owl, cat, snake can help us to eliminate some infectious diseases by killing mice. Even little insects play a very important role in bringing us a rich, musical and poetic world. Some like bees can make delectable honey; some have the same ability as birds to grasp injurious insects. However, some animals may eat as much grain as they like until farmers can harvest nothing from what they grow.
In short , every species has its reason for existing. Without them , the ecological system is destroyed and there will be no harmonious environment for man to live. People should learn to know the serious result.