名词
中文翻译：覆盖物
同义词：
['soil cover', 'soillayer']
例句：
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1. The dirtcover was thick enough to hide the tracks.
土层足够厚，可以掩盖痕迹。
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2.The farmer used a shovel todig up the dirt cover and plant newseeds.
农民用铲子挖开土层，种植新种子。
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3. Thedirt cover was so thickthat it made it difficult forus to see what was beneath.
土层太厚了，我们很难看到下面是什么。