动词
中文翻译：变硬
同义词：
['harden', 'harden up', "harden down例句：1. The sun's rays have begun to harden the earth's surface.（太阳的光线已经开始使地球表面变硬。）"]
例句：
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1. The sun's rays have begun to harden the earth's surface.
太阳的光线已经开始使地球表面变硬。
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2.The metal will harden when it is heated.
金属加热后会变硬。
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3.The ground hardened as the snow melted away.
随着雪融化，地面变硬了。