The outlet of a bicycle pump is used to inflate a football as illustrated in the diagram above. Why does the pressure of the air inside the pump increases as the pump handle is slowly pushed downward at constant temperature?

A. momentum of the air molecules are increased
B. volume occupied by the molecules is increased
C. frequency of collision of the air molecules with the walls of the pump is increased
D. more air molecules collide with one another in the system

Correct Answer: Option C

C. frequency of collision of the air molecules with the walls of the pump is increased