Red blood cells are packed with hemoglobin and each hemoglobin molecule requires four oxygen-binding iron atoms.

红细胞中充满了血红蛋白，而每个血红蛋白分子需要四个结合氧铁原子。

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Red blood cells are packed with hemoglobin and each hemoglobin molecule requires four oxygen-binding iron atoms.

红细胞中充满了血红蛋白，而每个血红蛋白分子需要四个结合氧铁原子。

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