它不仅是美国最长最深的石灰岩洞穴之一，也是世界上最长最深的石灰岩洞穴之一。
It's one of the longest and deepest limestone caves not just in the country but in the world.
在这种碳酸的帮助下，流动的水创造了世界上大部分的石灰岩洞穴。
With a little help from this carbonic acid, moving water forms most of the world's limestone caves.
据美国有线新闻网3日报道，一个国际科学小组宣布，他们在月球上发现了一个又大又深的垂直"熔岩洞"，可能适宜人类移民月球或修建月球基地。
An international team of scientists say they've discovered a protected lunar "lava tube" - a deep, giant hole - that might be well suited for a moon colony or a lunar base, CNN reported Sunday.
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