| A.They were formed in 1984.
B.They are at the top of two active volcanoes.
C.They are not like most other crater lakes.
D.Water in them turns over regularly.
（43）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.
43.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.
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.（44）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 pipe 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.