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来源：雅诚德英语网
Jupiter, Saturn, Uranus, and Neptune. Those are the gas giants, the four heavyweights of the solar system. But was there once a fifth?
木星、土星、天王星和海王星。这些都是气体行星，是太阳系的四个重量级。但曾经存在第五个行星吗？
Jupiter, Saturn, Uranus, and Neptune. Those are the gas giants, the four heavyweights of the solar system. But was there once a fifth?
木星、土星、天王星和海王星。这些都是气体行星，是太阳系的四个重量级。但曾经存在第五个行星吗？