How Is It That Humans Can Perceive Multiple Sounds at Once

How is it that humans can perceive multiple sounds at once?

A) because humans have two ears, each perceiving a subset of frequencies in the environment
B) because each portion of the basilar membrane vibrates at a unique frequency, and multiple regions can be stimulated at the same time
C) because the fluid in the middle ear can transmit multiple frequencies to the oval window
D) because the more frequencies of sounds that are present, the farther the sound travels into the cochlea