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  3. Scientists say there has been a severe decrease in the amount of water in Lake Chad in northern Africa in the last thirty years.

Scientists say there has been a severe decrease in the amount of water in Lake Chad in northern Africa in the last thirty years.

admin2009-04-23  47
问题     Scientists say there has been a severe decrease in the amount of water in Lake Chad in northern Africa in the last thirty years. They report that nature and humans share equal blame for this loss.
    In 1963 the fresh water lake covered twenty-five-thousand-square kilometers. Now the lake is only about five percent of that size. It measures only about one-thousand-three-hundred square kilometers in the dry season.
    Four nations surround Lake Chad. People in Niger, Nigeria, Chad, and Cameroon use it for water, fish and plant life.
    Michael Coe and Jonathan Foley are water experts at the University of Wisconsin in Madison. They reported about Lake Chad in the Journal of Geophysical Research. They say the area has suffered from a lack of heavy rain for more than thirty years. This has forced people to build systems to carry water to dry land. These irrigation systems further decrease the lake.
    Mister Coe says Lake Chad will be only a small body of water in the future. He says people still can get water from the lake to drink and for crops. But he says the lake will no longer provide a healthy environment for fish and plant life.
    The researchers used a computer to study what caused the water loss. Their computer study estimated the climate and amount of water in the area. The estimate started with the early 1960s. Then the researchers compared the estimates with the area’s recorded climate and water supply for the same period.
    The computer study showed results similar to the recorded ones for the first twenty years. But there was a big change in the 1980s. At that time, the lake got smaller much faster than the computer research had estimated.
    The researchers say major irrigation systems were built in the 1980s. The systems took water from two rivers that low into Lake Chad. The Chari and Logone rivers carry most of the water that enters the lake. The study showed the increased irrigation reduced the flow in the two rivers. Climate changes also were responsible for the reduction. Today the flow of the two rivers has been reduced by almost seventy-five percent.
    Scientists say the problem is expected to worsen in the coming years as the population and demand for water continue to increase.
选项 A、Demonstrating the serious weather condition around Lake Chad.
B、Introducing people’s activity around Lake Chad.
C、Analyzing of the factors that cause water decreases in Lake Chad.
D、Introducing scientists’ work about water condition in Lake Chad.
答案C
解析 主题题。A只是文中提及的自然因素；文中提及people’s activity只是为了说明人为因素；介绍科学家的工作也是为了分析原因。因此A,B,D均为错误答案。
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