41 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.
42 Without the greenhouse gases, the earth would
A become warmer.
B be much colder.
C move more slowly.
D move quickly.
43 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.
44 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.
45 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.