The earth's biosphere (the surface layer of the planet and the surrounding atmosphere) provides the land, air, water, and energy necessary to sustain life. This life-support system is a complex, interdependent one in which energy from the sun is changed into food for humans. The entire system depends on the sun, reasonably moderate temperature, and enough supplies of oxygen, pure water, and fertile soil. Since the earth's creation millions of years ago, the ecosystem has worked as an interdependent system relatively undisturbed by outside forces. But recently, especially since the Industrial Revolution, human beings have begun to disturb the balance of nature. Natural resources have been severely depleted (消耗) (forests have been destroyed, fertile land worn away, water polluted, and minerals used up), and the life-support system of air, water, and land has been poisoned by a variety of waste products and chemicals. The degree of these problems was noted in a report by the U.N. Developing Council on Environmental Quality. This report predicted that if present trends continue, the world will be more crowded and polluted and less stable ecologically and politically than the world we live in now. The twin problems of resource shortages and pollution are caused by three social forces.  First, the tremendous increase in population growth constantly increases the demand for food, energy, and other products. As the current population continues to increase, the stress on an already overburdened environment will be increased．A second source of the problem is the concentration of people in urban areas, where the ecosystem simply cannot absorb their waste products. Finally, environmental problems are worsened as more and more nations move toward modem development: an increased reliance on modern technology. As these nations become more technological, they will consume more energy, deplete more natural resources, and create more waste products than the biosphere can absorb. 小题1:The life-support system is composed of _____. A．air, water and land B．the earth, the sun and energy C．food, land and energy D．food, energy and the sun 小题2:The life-support system _____. A．change energy from the sun into food for humans B．depends on the sun for enough supplies of air, water and land C．exists in the surface layer of the earth and the surrounding atmosphere D．is a complex but independent system 小题3:The life-support system has been badly damaged by _____. A．natural forces B．human activities C．social movements D．political changes 小题4:The passage mainly talks about _____. A．the effects of Industrial Revolution on human beings B．the importance of life-support system to human beings C．the significance of balance of nature D．the destruction of life-support system and its causes