The next hundred years will be filled with other worldly adventures, exciting scientific discoveries, and danger, as humans leave Earth—perhaps forever.

　　Aging in Space

　　Suppose a space traveler is moving at a velocity of 186,200 miles per second. For every hour that passes for him, 30 hours pass on Earth. If he travels for a year in this fashion (having accelerated instantaneously) and then turns around and comes back at this speed (having turned around instantaneously), he will find that while he has seemed to himself to have traveled two years, the men on Earth would claim he had been absent for 30 years.

　　Suppose the space traveler had left at the age of 30, leaving behind a twin brother also aged 30. When he returned he would be 32, but his stay-at-home twin brother would be 60. That is why the “clock paradox”, is sometimes called the “twin paradox”.

　　Of course it takes quite a long while to accelerate to a high speed, and a long while to make a turn and head back again, so conditions aren’t quite as clear-cut as just described.

　　1.The giant, spherical spaceship mentioned in the passage is virtually the planet Earth.

　　2.According to the author, some persons have left the Earth and traveled into outer space within the past 25 years.

　　3.Scientists have already designed special space factories, which manufacture special products and tools for space use, such as medicine and perfect ball bearings.

　　4.According to the information of the passage, we can infer that if the Earth becomes too crowded or no longer suitable for men to dwell on someday, they’ll have to move into space.

　　5.The moon and the asteroids are alike with respect to their rich, valuable metals.

　　6.Ultraviolet light in space places scorches our skin as seriously as it does on Earth.

　　7.Even a short trip in outer space may do some damage to one’s brain.

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　　8.The reason some metal alloys can’t be made on Earth is that the heavier metals

　　together with the lighter ones.

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

　　10.According to the author, will be caused to a man in gravity�瞗ree space.