How Does the Ear Allow Humans to Distinguish the Volume

How does the ear allow humans to distinguish the volume of different sounds?

A) Louder sounds cause larger action potentials than softer sounds.
B) Louder sounds cause smaller action potentials than softer sounds.
C) Louder sounds induce a higher frequency of action potentials than softer sounds.
D) Louder sounds induce a lower frequency of action potentials than softer sounds.
E) Answers A and C are both correct.