D>

Clouds form in the atmosphere under a variety of conditions. There are clouds in the polar regions (where it is cold) as well as in the tropics (where it is warm). Radiative equilibrium has little to do with the processes by which an individual cloud forms. Sublimation is the transfer of water substance from the solid phase to the gaseous phase with no intermediate liquid phase. The common ingredient in the formation of ALL clouds is the fact that the air HAS TO RISE in order that it cool sufficiently to form a cloud. The correct answer is (c).