Timber swells when it is damp and shrinks when it is dry because it contains groups of atoms called hydroxyl groups, which absorb and release water.

木材在潮湿的时候就会膨胀，而干燥的时候会缩小，这取决于其中含有的氢氧基团，它可以吸收和释放水分。

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Timber swells when it is damp and shrinks when it is dry because it contains groups of atoms called hydroxyl groups, which absorb and release water.

木材在潮湿的时候就会膨胀，而干燥的时候会缩小，这取决于其中含有的氢氧基团，它可以吸收和释放水分。

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