单选题：The Exploding Lakes of Cameroon What comes to mind when you

The Exploding Lakes of Cameroon
What comes to mind when you think of a lake? You probably imagine a pretty scene withblue water，birds，and fish．For the people in the northwestern Cameroon，however, the image isvery different. For them，lakes may mean terrible disasters. In 1984，poisonous gases explodedout of Lake Monoun and came down into the nearby villages，killing thirty—seven people．Twoyears later,Lake Nyos erupted A cloud of gases rolled down the hills and into the valleys andkilled 1,700 people．
Lake Nyos and Lake Monoun are crater（火山口）lakes They were formed when watercollected in the craters of old volcanoes The volcanoes under Lake Nyos and Lake Monoun arenot active anymore. However, poisonous gases from the center of the earth continue to flow upthrough cracks in the bottom of the lake. This is normal in a crater lake. In most crater lakes，thesegases are released often because the water‘turns over’regularly．That is，the water from thebottom 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 thereason for this fact，but as a result，these lakes have more gases tapped at the bottom than othercrater lakes. In fact，scientists who have studied Lakes Nyos and Monoun have found 16,000times more gases．When a strong wind，cool weather a storm，or a landslide（滑坡）causes thewater 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 villagersto escape disaster. Now scientists from the United States，France，and Cameroon have found away to reduce the gas pressure at the bottom of Lake Nyos．They stood a 672-foot plastic pipe inthe middle of the lake，with one end of the pipe near the bottom and the other end in the air．Nearthe 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 shootsup through the pipe into the air like a fountain．With less pressure，a disastrous explosion is muchless 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 earlywarning systems at both lakes. If the gas pressure rises to a dangerous level，computers will setoff loud sirens（警报）and bright lights to warn the people in the villages．That way, t