在高海拔地区建机场，由于空气稀薄的原因，需要一个较长的跑道。
Airports at higher altitudes require a longer airstrip due to lower air density.
在空气稀薄的平流层中，如何产生升力是一个问题。 这种飞艇通过氢气浮力和空气动力制造升力的设计看上去能够解决这个难题。
Lift is a problem in the rarefied air of the stratosphere, and it seems such a design can help.
空气稀薄而清新，弥漫着朦胧的阳光与霜霭。
The air was thin and crisp, filled with hazy sunshine and frost.
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