Question

membrane - covered opening that separates the middle ear from the inner ear
oval door
oval gable
oval valance
oval banister
oval window

Explanation:

The oval window is a membrane - covered opening that separates the middle ear from the inner ear. It is an important structure in the auditory system. When the ossicles (malleus, incus, stapes) in the middle ear vibrate, they transmit the sound energy to the oval window, which then sets the fluid in the inner ear (cochlea) in motion.

Answer:

oval window