名词
中文翻译：Unknown
同义词：
['shell', 'outer layer例句：1. The scientist carefully removedthe outer covering of the sample to examineits structure.（科学家小心翼翼地移除了样本的外皮，以检查其结构。）']
例句：
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1. The scientist carefully removedthe outer covering of the sample to examineits structure.
科学家小心翼翼地移除了样本的外皮，以检查其结构。
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2. Theouter covering of the tree is made upof leaves and branches.
树的外皮由叶子和树枝组成。
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3. Theouter covering of the skinis essential for protection against theelements.
皮肤的外层对于抵御外界环境至关重要。