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:

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

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Environmental Science
The atmospheric greenhouse effect is produced mainly by the:

Absorption and re-emission of visible light by clouds
Absorption and re-emission of visible light by the ground
Absorption and re-emission of ultraviolet radiation by the atmosphere
Absorption and re-emission of infrared radiation by the atmosphere
Absorption and re-emission of visible light by the atmosphere

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