听力文本

The tighter the squeeze, the greater the chance of damaging some vital life-support system.
“瓶颈”越是狭窄，便越有可能损坏一些重要的生存设备。
In these conditions, a diver could easily become disorientated, and that could be fatal.
在这种情况下，潜水员很容易迷失方向，而这将导致送命。
The flooded caverns can play tricks on you in other ways.
地下水洞还会以别的方式戏弄你
What seems like air isn't. It's just another kind of water.
这看上去像是空气不对。它只是另一种水。
This is a halocline, a meeting of fresh and salt water.
这里是盐跃层，淡水与咸水的交汇处。

Fresh water from the jungle flows over the heavier salt water from the sea.
咸水来自海洋，比重较重，来自丛林的淡水在其上方流动。
The salt water layer is extremely low in oxygen,
咸水层的含氧量很低
making it a particularly difficult place for animals to live.
对动物而言是极为困难的生境
Yet some have managed it, like the remipede, one of the most ancient of all living crustaceans.
但有些动物却能在此生存，例如桨足虫--一种最古老的甲壳动物。

视频及简介

洞穴是不受阳光控制的生物栖息地之一，但这并不意味着那里就不存在野生生物。本集节目将深入洞穴内神秘而永恒的黑暗，探索山洞、洞穴和隧洞中未知的地下世界。