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     Scientists have found an unusual way to prevent our planet

from overheating: move it to a cooler spot. All you have to do is to

send a few comets (彗星) in the direction of Earth, and its orbit

will be changed. Our world will then be sent into a safer, colder

part of the solar system.

     This idea for improving our climate comes from a group of US

National Aeronautics and Space Administration( NASA) engineers

and American astronomers. They say their plan could add another

six billion years to the useful lifetime of our planet-effectively

doubling its working life.

     The plan put forward by Dr Laughlin, and his colleagues Don

Korycansky and Fred Adams, needs carefully directing a comet of

asteroid (小行星) so that it passes close by our planet and sends

some of its gravitational energy to Earth.

     "Earth's orbital speed would increase as a result and we

could move to a higher orbit away from the Sun," Laughlin said.

    Engineers would then direct their comet so that it passed

close to Jupiter or Saturn. The comet would pick up energy from

one of these giant planets. Later its orbit would bring it back to

Earth, and the process would be repeated.

     In the short term, the plan provides an ideal way to global

warming, although the team was actually concerned with a much

greater danger. The sun is certain to heat up in about a billion

years and so "seriously compromise" our biosphere (生物圈)-by

cooking us.

     That's why the group decided to try to save Earth.

     The plan has one or two worrying aspects, however. For a

stairt, space engineers would have to be very careful about how they

directed their asteroid or comet towards Earth. The smallest

miscalculation (误算) in orbit could fire it straight at Earth-with

deadly results.

    There is also the question of the Moon. As the scientific

American magazine points out, if Earth was pushed out of its current

position it is "most likely that the Moon would be stripped away

from Earth," it states. This would change our planet's climate.

1. If the plan is successful, Earth will have a working life of ____ years. 

A. 12 billion    

B. 6 billion

C. 18 billion    

D. 24 billion

2. What makes the scientists plan to save Earth? 

A. A few comets are moving to the direction of Earth.

B. Earth's working life is coming to an end soon.

C. Earth will become too hot for mankind to keep alive.

D. The moon is moving farther and farther away from Earth.

3. What does the underlined word" compromise" mean?   

A. provide                          

B. benefit

C. share                              

D. endanger

4. What serious problems might the plan cause according to the passage ?   

A. Earth might be moved too far away and man might be frozen to death.

B. The comet might hit Earth and man might lose the moon.

C. The comet might hit Jupiter or Saturn and never return toEarth.

D. Earth's working life might be greatly shortened.