名词
中文翻译：Unknown
同义词：
['underlay', 'underlayer', 'base layer']
例句：
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1. The floor is covered with a thick undertopping made of wood.
地板铺着一层厚厚的木制底层。
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2. The engineer decided to install an undertopping beneath the roof.
工程师决定在屋顶下安装一个底层。
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3. The construction workers laid down the undertopping before starting work on the walls.
建筑工人在开始砌墙之前铺设了底层。