2. 外语
  3. In terms of the evolution of life on Earth, human beings have just arrived. 【C1】______ their short time on Earth, however, peopl

In terms of the evolution of life on Earth, human beings have just arrived. 【C1】______ their short time on Earth, however, peopl

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问题     In terms of the evolution of life on Earth, human beings have just arrived. 【C1】______ their short time on Earth, however, people have brought about enormous changes to the surface of the planet—changes far out of【C2】______to the interval of time they have【C3】______ it.
    With the【C4】______ of intelligence and manual skill, people have found ways to use plant and animal resources, mineral ores, fuels, and so on. As the number of people on Earth increases, it becomes increasingly difficult for the population to survive【C5】______ the resources of the land. The amount of land is limited. Although agricultural production can be increased by use of【C6】______such as tractors and the addition of fertilizer, the land【C7】______can produce only so much food and no more. As the human population grows, people【C8】______ more.
    People are only a very small 【C9】______of all the living things on the planet. Yet their numbers create a 【C10】______ on resources that can’t be 【C11】______. For example, the amount of water on Earth is limited; this water is 【C12】______ through natural processes. However, the natural processes for 【C13】______ water can clean only a certain amount of water.【C14】______, a limited amount of petroleum can be found under the Earth’s surface.
    All natural systems tend toward 【C15】______ among opposing factors or forces. Human activities can cause or 【C16】______ permanent changes in natural systems. The【C17】______ smoke from thousands of factories has caused enormous air pollution. Cleaning this smoke has【C18】______ the protective ability of natural processes. The forests cannot clean the air fast enough. The twentieth century began with powerful countries competing to take【C19】______ of the Earth. As an outcome of their hunger, the Earth was abused. Now that people are no longer【C20】______ of the causes of the sickness of our planet, they seek ways to rescue the Earth.
【C15】
选项 A、future
B、extreme
C、limit
D、balance
答案D
解析 名词辨析题。自然体系要在各种对立因素中达到平衡，所以[D]balance是答案。
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