问题
填空题
电磁铁的磁性有无可以由______ 来控制，电磁铁的磁性强弱可以由______ 来控制，电磁铁的南北极可以由______ 来控制。
答案
通断电，电流强弱，变换电流方向
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电磁铁的磁性有无可以由______ 来控制，电磁铁的磁性强弱可以由______ 来控制，电磁铁的南北极可以由______ 来控制。
通断电，电流强弱，变换电流方向
| 任务型阅读： 阅读下面的短文，完成表格。 | ||||||||||
| In the past, man did not have to think about the protection of his environment. There were not many people on earth, and natural resources (资源) seemed to be unlimited (无限的). Today, things are different. The world has become too crowded (拥挤的). We are using up our natural resources too quickly, and at the same time we are polluting our environment with dangerous chemicals. If we continue like this, human life on earth will not survive. Everyone realizes today that if too many fish are taken from the sea, there will soon be none left. Yet, with modern fishing methods (方法), more and more fish are caught. We know that if too many trees are cut down, forests will disappear and nothing will grow on the land. We realize that if rivers are polluted with waste products from factories, we will die. However, in most countries, waste products are still put into rivers or into the sea, and there are few laws to stop this. We know, too, that if the population (人口) of the world continues to rise at the present rate, in a few years, there will not be enough food. What can we do to solve these problems? If we eat more vegetables and less meat, we will easily get more food. Land that is used to grow crops can feed five times more people that land where animals are kept. The world population will not rise so quickly if people use modern methods of birth control. Finally, if we educate people to think about the problems, we shall have a better and cleaner living place in the future. | ||||||||||
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