Environmental Science
Man made sources of radiation pollution are:

all of these
explosion of nuclear weapons
nuclear fuels and preparation of radioactive isotopes
mining

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Environmental Science
Low clouds retard surface cooling at night better than clear skies because:

The clouds absorb and radiate infrared energy back to earth
The clouds start convection currents between them
The clouds are better conductors of heat than is the clear night air
The water droplets in the clouds reflect infrared energy back to earth
The formation of the clouds releases latent heat energy

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