The space is left to let the rail expand when it gets hot.

缝隙是留给铁轨发热膨胀用的。

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Because things get expand when they heated, hot water is actually HEAVIER than cold water.

因为物体遇热膨胀，所以热水其实要比冷水重。

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Wooden doors expand in hot, wet weather.

木门在潮热天气会膨胀。

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Iron bulge expand to hot.

铁受热膨胀。

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Iron bulge expand to hot.

铁受热膨胀。

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