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| 21. | If a satellite can one day be put into orbit round Mars, scientists will be able to find out a great |
| 如果有一天,人造卫星能被发射到围绕火星的轨道上去,科学家们将会发现很多情况。 |
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| 22. | Even a telescope in orbit round the earth, like the very successful Hubble telescope, would not be suitable |
| 即使是一台放置在围绕地球的轨道上的望远镜——如非常成功的哈勃望远镜——也因为太阳系中的尘埃微粒而无法胜任。 |
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| 23. | Alternatively, if the star were small, the life-supporting planet would have to have a close orbit round |
| 反之，如果恒星很小，维持生命的行星就要在离恒星很近的轨道上运行，而且要有极好的条件才能使生命得以发展。 |
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