What Is the Primary Function of the Round Window of the Cochlea

What is the primary function of the round window of the cochlea?

A) To transmit sound from the middle bones of the ear to the fluid filled cochlea.
B) To transmit sound from the outer ear to the bones of the middle ear.
C) To allow for displacement of the ear drum by relieving pressure in the middle ear.
D) To allow for displacement of the oval window by relieving pressure in the cochlea.