Clouds usually form on the windward side because this is where air a. rises and cools. b. rises and warms. c. sinks and cools. d. sinks and warms.

a. rises and cools.

Explanation:

The windward side of any mountain or an island, is the side where the prevailing wind, which carries moisture laden air, faces the mountain or island, thereby causing the wind to rise. This side of the mountain or island where the prevailing wind rises is the cold part where clouds are formed as the prevailing rising wind cools. This clouds later result into rain. The windward side is the cooler and wetter side of a mountain or island.