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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（向心的）force. The moon and Mars could become new sources of new materials. Driving through space will no --78. longer need Earth fuel-the energy would come from the sun. This energy would be converted from --79. electricity to work magnetic rockets. That all sounds quiet fantastically but, with --80. the rapid development of modern technology, who knows about what the future holds? 答案：71. sort -- short 72. launch -- launched 73. it -- which 74. crews -- crew 75. Upon --- Once 76. rotation -- rotate 77. inward -- outwards 78. will -- would 79. from -- into 80. fantastically -- fantastic | 
