单选题 Are we at the beginning of another Age of Exploration? Perhaps even more important, are we at the beginning of 1 Age of Colonization? As the population of the world increases towards the point 2 the earth can no longer support all the people 3 on it, the second question becomes urgent. Will we discover a new world, 4 Columbus did, on which human life will be possible? At this point in the space age, no one can really answer these questions. We can say, 5 that we will not see tomorrow the kind of space travel that 6 fiction and the movies have shown. It will be a long time before we have flight that run 7 to human colonies on the moon or on, one of the planets. We are not even going to be able to 8 immediate advantages of the minerals that we may find on the planets 9 our own solar system.
Great problems must be solved 10 we could send colonists out into place. The distances that must be 11 and the length of time it takes to do that can hardly be 12 . There are also dangers that we still do not realty understand, from radiation, for example, or from pieces of matter 13 in space, or from contamination forms of life that might 14 there. There is also need for humans to take their own environment into space 15 them. So far no "island" has been discovered in space on which people can exist without systems that 16 life, and these systems must accompany any future space 17 Finally, on the most practical 18 there has to be enormous expense 19 in space exploration. The U.S. and Russian governments have already spent billions of dollars for projects 20 which they can receive a return only in knowledge and not in money.