木卫一的表面能常保年轻，是因为它有许多活火山。

The unusual surface of Io is kept very young by its system of active volcanoes.

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木卫一和木卫二跟地球所见的月亮是相同的大小。

The Jovian Io and Europa are about the same size as Earth's moon.

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木卫一和木卫二跟地球所见的月亮是相同的大小。

The Jovian Io and Europa are about the same size as Earth's moon.

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