Atoms of iron in the nail combine with atoms of oxygen from the air to form molecules of iron oxide, or rust.

钉子里的铁原子与空气中的氧原子结合后形成氧化铁分子，也就是锈。

柯林斯例句

They get oxygen from the air, so they must return to the surface regularly to breathe.

它们从空气中获得氧气, 所以它们必须不时地回到海面上呼吸.

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