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  3. 共用题干 第二篇The Exploding Lakes of CameroonWhat comes to mind when you think of ...

共用题干 第二篇The Exploding Lakes of CameroonWhat comes to mind when you think of ...

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问题 共用题干
第二篇

The Exploding Lakes of Cameroon

What comes to mind when you think of a lake?You probably imagine a pretty scene with blue water,birds,and fish.For the people in the northwestern Cameroon,however,the image is very different. For them,lakes may mean terrible disasters.In 1984,poisonous gases exploded out of Lake Monoun and came down into the nearby villages,killing thirty-seven people.Two years later,Lake Nyos erupted.A cloud of gases rolled down the hills and into the valleys and killed 1,700 people.
Lake Nyos and Lake Monoun are crater（火山口）lakes. They were formed when water collected in the craters of old volcanoes.The volcanoes under Lake Nyos and Lake Monoun are not active anymore.However,poisonous gases from the center of the earth continue to flow up through cracks in the bottom of the lake.This is normal in a crater lake.In most crater lakes,these gases are released often because the water"turns over"regularly.That is,the water from the bottom of the lake rises and mixes with the water at the top,allowing the gases to escape slowly.
However,in Lakes Nyos and Monoun,there is no regular turning over. No one knows the reason for this fact,but as a result,these lakes have more gases trapped at the bottom than other crater lakes.In fact,scientists who have studied Lakes Nyos and Monoun have found 16,000 times more gases. When a strong wind , cool weather, a storm, or a landslide（滑坡）causes the water to turn over suddenly,the gases escape in a violent explosion.
In the past,no one knew when the gases might explode,so there was no way for the villagers to escape disaster. Now scientists from the United States,France,and Cameroon have found a way to reduce the gas pressure at the bottom of Lake Nyos.They stood a 672-foot plastic pipe in the middle of the lake,with one end of the pipe near the bottom and the other end in the air. Near the top of the pipe,the team put several holes that could be opened or closed by a computer. Now,when the gas pressure gets too high,the holes are opened and some of the gas-filled water shoots up through the nine into the air like a fountain.With less pressure,a disastrous explosion is much less likely.However,the scientists are not sure that one pipe will be enough to prevent explosions.They hope to put in others soon and they plan to install a similar pipe and a computer system at Lake Monoun as well.
To protect people nearby until all of the pipes are in place,the scientists have installed early warning systems at both lakes.If the gas pressure rises to a dangerous level,computers will set off loud sirens（警报）and bright lights to warn the people in the villages. In that way,they will have time to escape from the dangerous gases.
选项 Lake Nyos and Lake Monoun explode because________.
A:the gases rise to the top and mix with air
B:people from the villages turn over the water
C:scientists have put in a computer system
D:they have more gases trapped at the bottom than other crater lakes
答案D
解析第一段提到，“ poisonous gases exploded out of Lake Monoun”,所以选B，有毒气体会突然喷发。
选项A、B和D的信息不完整或者错误，第二段和第三段开头分别提到 “They were formed when water collected in the craters of old volcanoes…there is no regular turning over”，这是两个湖与众不同的地方，所以选C。
第三段说到两个湖时，提到“these lakes have more gases trapped at the hottom than other crater lakes”，这就是湖泊爆炸的原因。
文章第四段第三句提到科学家们“stood a 672-foot plastic pipe in the middle of the lake ” , “ erect”和“stand”为同义词，表示“树立、立起”。
最后一段提到“the scientists have installed early warning systems at both lakes”，看来灾难是可防可控的，因此选D。
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