An air mass's relative humidity is a measure of how much water vapor it contains compared to how much it can contain. Different types of air masses, with different temperatures and pressures, are able to hold different amounts of water vapor. What could cause the relative humidity of an air mass to change?

D. all of these

Explanation:

The relative humidity is usually defined as the concentration of water vapor that can be stored in the air in order to get saturated at any given temperature. It is commonly expressed in terms of percentage (%).

The relative humidity is controlled by two factors namely-

(A) Air temperature

(B) Amount of water vapor in the air

Temperature plays an important role in controlling the relative humidity of the air. As the temperature increases, the air increases its capacity to hold more amount of water vapor. The warm air is comprised of higher moisture content in comparison to the cold air, so they contain high relative humidity.

These are the two factors that are responsible for the cause of changes in the relative humidity.