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The pure white nests of cave swiftlets are the main ingredient of bird's nest soup
洞金丝燕的纯白燕窝是燕窝羹的主要成分
and, gram for gram, are worth as much as silver.
每克燕窝的价值堪比白银
As soon as its nest is removed, a bird will immediately build another,
燕窝被摘去后，金丝燕很快又会再吐一个
so as long as this valuable harvest is properly controlled, the colonies will continue to flourish.
所以，只要这种利润可观的采摘行为得到适当控制，燕群仍旧可以长盛不衰。
These Bornean caves are among the biggest in the world
婆罗洲的这些洞窟是世界上最大的洞穴
and they're still getting bigger as, each year, rainwater eats away a little more limestone.
它们仍在不断扩大，因为每年雨水都会侵蚀掉少许石灰岩。
But water in caves doesn't only erode, it also builds.
可是洞里的水不光只是侵蚀，它们还能造景。
This water is loaded with dissolved limestone,
这些水中含有溶解的碳酸钙
and when it meets the air in the cave, some of that is deposited as a mineral, calcite.
当它与洞内空气接触时，其中的一些就会沉淀为一种矿物，方解石。
As it builds up, so the calcite forms decorations that hang from the ceiling, stalactites.
随着它的积累，方解石形成了悬在洞顶上的装饰物，钟乳石。
Each drop leaves behind only a minuscule amount of calcite,
每滴水珠只会留下极少量的方解石微粒
but over time, the process can produce some spectacular results.
但随着时间的推移，它们变成了最引人入胜的景观。
