Environmental Science
Much of Tibet lies at altitudes over 18,000 feet where the pressure is about 500 mb. At such altitudes, the Tibetans are above roughly:

50% of the air molecules in the atmosphere
10% of the air molecules in the atmosphere
25% of the air molecules in the atmosphere
75% of the air molecules in the atmosphere

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Environmental Science
Frost forms when:

The dew point is 32oF or below.
All of these
Objects on the ground cool below the dew point temperature.
Water vapor changes into ice without first becoming a liquid.

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