英语四级改错练习题
　　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 [51] 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 [52] April 1981. This was ""Columbia"", it made several [53] 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 being used to bring the crews back to earth.[54]
　　Upon established, each space station will [55] generate its own atmosphere and have its own agriculture. It will need to rotation to provide [56] an artificial gravity; people will be forced inwards [57] from the centre by centrifugal force.
　　The moon and Mars could become new sources of new materials. Driving through space will no [58] longer need Earth fuel - the energy would come from the sun. This energy would be converted from [59] electricity to work magnetic rockets.
　　That all sounds quite fantastically but, with [60] the rapid development of modern technology, who knows about what the future holds?

　　答案
　　51. and lack of... short 52. bus launch in... launched 53. it made several... which 54. the crews back... crew 55. Upon established... once 56. to rotation to... rotate 57. forced inwards... outwards 58. space will no... would 59. converted from... into 60. quite fantastically but... fantastic