题目

阅读下面短文，根据其内容写一篇60词左右的内容概要。     For thousands of years, people have tried to control water by building dams. Dams allow people to collect and store water for use at home, in industry, and in agriculture. For example, when people build a dam on a river, a reservoir(水库) collects water that can be channelled for human needs. In addition, the ability of dams to control water flow helps prevent floods. Dams can also be used to make electricity.     As the human population grows, the need for water and electricity increases. So many new dams have been built in the past 50 years. Today, nearly half of the rivers in the world have at least one large dam. If managed well, dams can be a great benefit to people. Some dams, however, may do more harm than good.     All dams cause changes in river ecosystem that has an impact on surrounding land and people. As river water collects behind a large dam, it may back up and form a large lake, flooding land and killing plants and animals. People living on land upstream of a dam may be forced to abandon their homes. Below the dam, water flow decreases. This changes the downstream ecosystem. Plants and animals may not have enough water. Some types of fish may be unable to move upstream to reproduce. Rare species of plants and animals may become endangered. Farmers living downstream from the dam may not be able to grow crops. People who fish for a living may have to find other work.     An independent organization called World Commission on Dams worked during the late 1990s to suggest ways of reducing problems caused by some large dams. The commission recommended that the research, the group decision-making, and the creation of a plan all take place before the start of construction of a large dam. For a plan to be successful, it would need to demonstrate that the dam would contribute to the long-term improvement of human life. The likely impact of the dam on local people and the environment would be assessed and considered in the decision-making process. 答案：   People have built dams on rivers to control water for thousands of years. Water collected from the dams can be used in many ways and it does a lot of good to humans. However, the dams also cause many problems, both to the environment and to humans themselves. To reduce problems caused by the dams, the WCD(World Commission on Dams) has been founded to make useful suggestions.

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