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
44 A team of scientists has
A erected a pressure-releasing pipe in the lake
B identified the gases at the bottom of the lake
C built a beautiful fountain near the lakes
D removed all dangerous gases from the lakes
45 What do we learn from the last paragraph?
A Scientists are planning to install pipes in all crater lakes.
B Scientists still do not know how to prevent gas explosions
C Explosion disasters could be avoided in the future
D Warning systems have been set up in the villages nearby.
参考答案：
41 B 该题问的是Nyos和Monoun两湖喷发时会出现什么情况?第一段第五句提到，Monoun喷发时有毒气体随之而出。两年后，Nyos湖喷发时也出现类似情况。故B为答案。
42 c 本题为细节题。问的是关于Nyos和Monoun两湖哪句陈述是正确的?选项A说的是两湖于1984年形成的，不符合原文意思。选项B的意思是：他们坐落在两座活活火山上，也与原文意思不符。选项D说的是湖中的水定期翻滚，均与原文不符。只有选项c正确。
43 D 题句的意思是：Nyos和Monoun两湖发生喷发的原因是什么?前三个选项均与原文意思不符，答案见第三段第二句。
44 A 本题问的是一队科学家干了什么工作?第四段第三句提到他们在湖里立了一根释放湖底气压的管子。故A为答案。
45 c 本题问的是在文章最后一段我们了解到了什么?文章最后一段主要讲的是在所有的湖里竖起缓解湖底气压的管子后，就不会有危险。故选项c为正确答案。