Now one of the challenges of going up to altitude is when you get to 30,000 feet -- it's great, isn't it? -- When you get to 30,000 feet you can really only use oxygen.
目前上升到这样的高度的挑战之一是 当你到达3万英尺时--这非常高，不是么？-- 当到达3万英尺时，你真的只能依靠氧气瓶了。