动词
中文翻译：使变硬
同义词：
['harden', 'stiffen', "harden例句：1. The old man's joints were stiffening as he grew older.（随着老人年龄的增长，他的关节开始变得僵硬。）2. The ground was too soft to walk on", 'so we had to stiffen it with wood planks.（地面太软了，走不了，所以我们用木板加固了它。）']
例句：
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1. The old man's joints were stiffening as he grew older.
随着老人年龄的增长，他的关节开始变得僵硬。
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2. The ground was too soft to walk on, so we had to stiffen it with wood planks.
地面太软了，走不了，所以我们用木板加固了它。
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3. As the weather turned colder, the leaves began to stiffen and turn brown.
随着天气变冷，树叶开始变硬并变黄。