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. Which of the following could cause the relative humidity of an air mass to change?
A.
a change in its water vapor content
B.
a change in its pressure
C.
a change in its temperature
D.
all of these