Everyone knows Earth has one moon. That's why it's called 'the moon'. It goes around our planet. People have gone to the moon in rockets. How do we know something is a moon? It goes around and around a planet or something that isn't a star.

地球只有一個月亮，但只要不斷繞著行星，又不是星星的物體就叫月亮，所以外太空裡有很多顆。

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