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第八篇： Error Correction Some people, in all seriousness, say that humans will be living in space within the next hundred or so years. Planet Earth will be crowded, dirty and lack of resources. A sort of exodus --71. of mankind will begin. Spaceships will be assembled so that they revolve around the earth. Some may orbit around Mars. These space stations will be serviced by space buses. We saw the first space bus launch in --72. April 1981. This was Columbia, it made several --73. orbits around the earth and then returned, landing on a huge dry lake bed in California. Columbia will be used again. Previous spaceships have been abandoned, only the nose cone being used to bring the crews back to earth. --74. Upon established, each space station will --75. generate its own atmosphere and have its own agriculture. It will need to rotation to provide --76. an artificial gravity; people will be forced inwards --77. from the center by centrifugal force. The moon and Mars could become new sources of | 
