And with good reason. 以及它形成的原因

179. that we've come to appreciate the full significance and scale of these flooded passageways.
     我们才能完全了解 这些地下水道的重要性及其规模
180. So far, more than 350 miles of underwater galleries in the Yucatan have been mapped,
     人们迄今为止已绘制了350英里的 尤卡坦半岛地下水系图
181. but still nobody yet knows the true extend of this subterranean waterworld.
     但仍旧无人知晓 这个地下水世界究竟有多大
182. And with good reason.
     以及它形成的原因
183. Underwater caving is notoriously dangerous.
     地下水洞是出了名的危险
184. When the nearest exit may be hundreds of metres or more away,
     最近的出口可能远在 几百米之外或者更远的地方
185. running out of air down here would be fatal.
     在这里 耗尽氧气将是致命的

来自《行星地球 第一季 第四集 Planet Earth S01E04 洞穴》第 182 行