1 According to the passage， a greenhouse is built to
A keep the plants warm.B prevent air pollution.
C stop the greenhouse effect.D produce useful gases.
2 Without the greenhouse gases， the earth would
A become warmer.B be much colder.
C move more slowly.D move quickly.
3 A major cause of the increase in the greenhouse gases is
A the burning of trees and crops.
B the building of many greenhouses.
C the burning of large quantities Of coal and oil.
D the flooding of large areas of the world.
4 According to the passage， chlorofluorocarbon gases differ from carbon dioxide in that
A they are more useful. B they are much heavier.
C they are more efficient in making the' world colder.
D they are more effective in catching the heat from the sun.
5 A small increase in the earth's temperature may bring about
A a decline in agriculture. B a drop of the sea level.
C the death of all animals. D a delay in the greenhouse effect.
【参考答案】
1. A 2. B 3. C 4. D 5. A
