动词
中文翻译：使变硬
同义词：
['solidify', 'harden', 'toughen']
例句：
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1.The ice on the lake has hardened into a thin layer of snow.
湖上的冰已经变硬，变成了一层薄薄的雪。
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2. As the weather gets colder, it's important to harden your car's tires.
随着天气变冷，重要的是要给汽车轮胎打气。
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3.The old tree had hardened its bark over time.
这棵老树的树皮随着时间的推移而变得更坚硬。