2009年6月大學(xué)英語四級全真預(yù)測試題及答案

　　Other scientists have designed space colonies, complete with farms, schools, and artificial day and night. Hundreds, or even thousands, of people will live, work, play—even go to school, far above the Earth.

　　Our conquest of space, of course, has already begun. We have explored part of the Moon, sent robot spaceships onto the surface of Venus and Mars, and aimed space probes past the planets of Jupiter and Saturn.

　　Last June, one robot ship, Pioneer 10, left our solar system forever. And astronauts from both the Soviet Union and the United States have lived in space stations.

　　The conquest of space, without question, is one of the greatest adventures human beings have ever set out on. But it may be more than a great adventure. Some scientists think the conquest of space may be a necessity for survival of the human species.

　　We are tearing up more and more of the Earth to get raw materials for industry. And we are polluting the air and water as we manufacture products that we need or want. Almost everything that seems to make our lives more comfortable, and from electricity to pesticides, uses up or alters a piece of our planet’s natural environment.

　　Why Go into Space?

　　Yet our solar system is full of resources. The moon is chockfull of valuable metals. So are the asteroids, the small, rocky, planet-like bodies orbiting the sun most of them between Mars and Jupiter. These metals, if we can get them, could be used to build factories and space stations.

　　Also, in space, there is no atmosphere to filter out the sun’s energy. There is plenty of solar energy to be turned into electricity for manufacturing, for creating comfortable living conditions.

　　Getting away from Earth has other advantages, too. Modern industry uses many kinds of metal alloys (mixtures of metal that are better for certain purposes than pure metals). Yet some metal alloys either can’t be made or are very expensive to make on Earth because of gravity. For instance, certain metals don’t mix well on Earth. But in zero gravity, molten (hot, liquid) metals mix more evenly. This is because there is no gravity to pull the heavier metals down, while the lighter ones float on top.

　　From space, too, we can look down on the Earth and study the atmosphere, its weather, and the effects of air pollution.

　　And because there is no strong gravity to break free from, our future homes away from Earth will be convenient starting points for travel to distant planets.

　　But, while going into space might solve some problems, outer space can also be a dangerous place. For example, in outer space, we have to protect ourselves from the dangers of ultraviolet light and cosmic rays. Ultraviolet light from the sun can give us bad sunburns right here on Earth. Yet, Earth’s atmosphere screens out most of that harmful radiation. Cosmic rays are tiny high�瞖nergy particles from outer space. Again, the Earth shields us from most of them.

　　At Home in Space?

　　But in space, without special protection, we would be exposed to much stronger radiation from ultraviolet light and cosmic rays. Also, in the zero gravity of outer space, our bones will lose calcium and become weaker. This will be more of a problem the longer people stay out in space. Doctors are looking for a way to keep our bones from losing calcium in outer space. And a small spaceship just might “drive you batty” after a while. But even on a short trip in outer space, you might not feel as well as you’d like to. Space travel could make you seasick!

　　Yet, these risks won’t keep people from going into space. Eventually, an Earth-like environment will be built in space. And they will be populated by people with many different interests: medicine, construction, farming, teaching, mining, and so on.