On a night when the sky is clear, the temperature may dip considerably. On a cloudy night the temperature will usually dip much less. The reason for this difference is that......

• A. the clear sky allows radiant energy to escape readily from the earth
• B. on a cloudy night the clouds are warm and therefore retard the cooling
• C. the clear sky allows the cold of outer space to reach the earth
• D. current of air carry the heat away from the earth on a clear night