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 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.
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." That way, they will have time to escape from the dangerous gases.
11 What will happen when Lake Nyos and Lake Monoun explode?
A Water will flow down the hills.
B Poisonous gases will be released suddenly.
C A strong wind will rise from the lakes.
D The volcanoes will come to life.
12 Which of the following statements about Lake Nyos and Lake Monoun is true?
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.
13 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
14 Ateam 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.
15 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.
答案：
1. C 2. C 3. A 4. C 5. D
6. A 7. C 8. D 9. B 10. C
11. B 12. C 13. D 14. A 15. C
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第5部分：补全短文(第46～50题，每题2分，共10分)
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Death control
A very important world problem-in fact, I am inclined to say it is the most important of all the great world problems______(1) ____-is the rapidly increasing pressure of population on land and on land resources.
This enormous increase of population will create immense problems. By 2000 A.D., unless something desperate happens, there will be as many as 7,000,000,000 people on the surface of the earth! So this is a problem which you are going to see in your lifetime
Why is this enormous increase in population taking place? It is really due to the spread of the knowledge and the practice of _____ (2)____. You have heard of Birth Control? Death Control is something rather different. Death Control recognizes the work of the doctors and the nurses and the hospitals and the health services in keeping alive people who,_____(3)_____, Would have died of some of the incredibly serious killing diseases , as they used to do. Squalid conditions, which we can remedy by an improved standard of living, caused a lot of disease and dirt. Medical examinations at school catch diseases early and ensure healthier school children. Scientists are at work stamping out malaria and other more deadly diseases. If you are seriously ill there is an ambulance to take you to a modern hospital. Medical care helps _____(4)______. We used to think seventy was a good age; now eighty, ninety, it may be , are coming to be recognized as a normal age for human beings. People are living longer because of this Death Control, and _____(5)_____, so the population of the world is shooting up.
A fewer children are dying
B a few years ago
C what is coming to be called Death Control
D which face us at the present time
E making it possible for people to live longer
F to keep people alive longer
答案：
1. D 2. C 3. B 4. F 5. A
第6部分：完形填空
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A Biological Clock
Every living thing has what scientists call a biological clock that controls behavior. The biological clock tells __1__ when to form flowers and when the flowers should open. It tells __2__ when to leave the protective cocoon and fly away, and it tells animals and human beings when to eat, sleep and wake.
Events outside the plant and animal __3__ the actions of some biological clocks. Scientists recently found, for example, that a tiny animal changes the color of its fur __4__ the number of hours of daylight. In the short __5__ of winter, its fur becomes white. The fur becomes gray brown in color in the longer hours of daylight in summer.
Inner signals control other biological clocks. German scientists found that some kind of internal clock seems to order birds to begin their long migration __6__ twice each year. Birds __7__ flying become restless when it is time for the trip, __8__ they become calm again when the time of the flight has ended.
Scientists say they are beginning to learn which __9__ of the brain contain biological clocks. An American researcher, Martin Moorhead, said a small group of cells near the front of the brain __10__ to control the timing of some of our actions. These __11__ tell a person when to __12__, when to sleep and when to seek food. Scientists say there probably are other biological clock cells that control other body activities.
Dr. Moorhead is studying __13__ our biological clocks affect the way we do our work. For example, most of us have great difficulty if we must often change to different work hours. __14__ can take many days for a human body to accept the major change in work hours. Dr. Moorhead said industrial officials should have a better understanding of biological clocks and how they affect workers. He said __15__ understanding could cut sickness and accidents at work and would help increase a factory's production.
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