名词
中文翻译：空壳
同义词：
['shell', 'casing', 'outer shell']
例句：
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1. The egg is a hard shell that protects the egg inside.
鸡蛋是硬壳，保护了蛋里面的。
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2. The shell of the turtle is made up of two layers.
乌龟的壳由两层组成。
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3. The shell is used to store food and water for the baby turtle.
壳用来储存食物和水给小乌龟。