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题目材料：
Simulations indicate, and observations confirm, that the particles constituting Saturn's rings are giving up angular momentum to moons of the planet. The simulations predict that over just a few hundred million years, the related energy transfer will cause the rings' collapse. An analogous process occurs around young stars in the disks of matter from which planets emerge, and these protoplanetary disks do vanish that quickly, computer models show. Yet if Saturn's rings are so short-lived, a large comet or moon―the rings' presumed source一must have broken apart in Saturn's vicinity within the past several hundred million years. That is quite unlikely. It would have been much more probable in the young solar system—4 billion years ago or more.
以上解析由 考满分老师提供。
