Environmental Science
At night, low clouds:

Have no effect on the atmospheric greenhouse effect
Are often caused by the atmospheric greenhouse effect
Weaken the atmospheric greenhouse effect
Enhance the atmospheric greenhouse effect

ANSWER DOWNLOAD EXAMIANS APP

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

ANSWER DOWNLOAD EXAMIANS APP