Passage 2
The molecules of carbon dioxide in the Earth’s atmosphere affect the heat balance of the Earth by acting as a one-way screen. Although these molecules allow radiation at visible wavelengths, where most of the energy of sunlight is concentrated, to pass through, they absorb some longer wave- length, infrared emissions radiated from the Earth’s surface, radiation that would otherwise be transmitted back into space. For the Earth to maintain a constant average temperature, such emissions from the planet must balance incoming solar radiation. If there were no carbon dioxide in the atmosphere, heat would escape from the Earth much more easily. The surface temperature would be so much lower that the oceans might be a solid mass of ice.
Today, however, the potential problem is too much carbon dioxide. The burning of fossil fuels and the clearing of forests have increased atmospheric carbon dioxide by about 15 percent in the last hundred years
A. Objective yet concerned.
B. Angry yet resigned.
C. Completely detached.
D. Incredulous.
In July 1994 Jupiter, the largest planet in our solar system, was struck by 21 pieces of a comet (彗星). When the fragments (碎片) landed in the southern part of the giant planet, the explosions were watched by scientists here on earth. But what if our own planet was hit by a comet
The year is 2094. It has been announced that a comet is heading towards the Earth. Most of it will miss our planet, but two fragments will probably hit the southern part of the Earth. The news has caused panic.
On 17 July, a fragment four kilometers wide enters the Earth’s atmosphere with a huge explosion. About half of the fragment is destroyed. But the major part survives and hits the South Atlantic at 200 times the speed of sound. The sea boils and an enormous wave is created and spreads. The wall of water rushes towards southern Africa at 800 kilometres an hour. Cities on the African coast are totally destroyed and millions of people are drowned. The wave moves into the Indian Oce
A. Because they could only live in the warm climate.
B. Because they once dominated the earth.
C. Because their extinction indicates future disasters.
D. Because dinosaurs and humans never live in the same age.
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