Environmental Science
Frost forms when:

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

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Environmental Science
Although the polar regions radiate away more heat energy than they receive by insolation in the course of a year, they are prevented from becoming progressively colder each year by the:

Circulation of heat by the atmosphere and oceans
The insulating properties of snow
Conduction of heat through the interior of the earth
Concentration of earth's magnetic field lines at the poles
Release of latent heat to the atmosphere when polar ice melts

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