在条件许可之下，一般都在海拔以上离地面750到1500英尺范围内的均匀高度上飞行。
It is customary to fly , so far as is feasible, at a uniform elevation above sea level but within a range of 750 to 1500 ft above the earth's surface.
在这座山的北面，海拔900米以上的位置有一个非常重要的纯净水水源地。
More than 900 metres high, on the mountain's north face, lies an all-important source of pure water.
海拔4000米以上是高山寒漠：砾石、石头和岩石。
Above 4,000 meters is the highland desert: gravel, stones, and rocks.
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