名词
中文翻译：空洞
同义词：
['cavity', 'hollow', 'void']
例句：
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1.The tree has many hollows where birds nest.
这棵树有很多鸟巢，里面是空的。
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2.The cave was filled with darkness and the sound of dripping water.
这个洞穴里一片漆黑，还有滴水的声音。
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3.The hollow in the wall is a perfect place for hiding.
墙里的洞是个完美的藏身之处。