Clouds usually form when moist air rises because A. the air pressure increase
B. the dew point decrease
C. the air is cooled to its dew point
D. additional water vapor is added to the air

Clouds form when moist air rises because:

D.

Explanation:

Clouds form when moist, warm rising air cools and expands in the atmosphere. The water vapor in the air condenses to form tiny water droplets which are the basis of clouds.