Final answer:
The Cochlea is the structure located in the inner ear; it helps convert sound into nerve signals. The eardrum, ossicles, and Eustachian tube are part of the middle ear, not the inner ear. The cochlea works with other inner ear structures to control hearing and balance.
Step-by-step explanation:
The structure located in the inner ear is the D) Cochlea. The cochlea is a fluid-filled, snail-shaped structure that is responsible for converting sound waves into nerve impulses that are sent to the brain. It is found in the inner ear along with the vestibule and semicircular canals, which are involved in balance.
The other options provided, A) Ear drum, B) Ossicles, and C) Eustachian tube, are all components of the middle ear. The eardrum, also known as the tympanic membrane, vibrates upon receiving sound waves.
The ossicles, which include the malleus (hammer), incus (anvil), and stapes (stirrup), help amplify and transfer these vibrations to the cochlea. The Eustachian tube connects the middle ear to the pharynx and helps equalize pressure in the middle ear with the external atmospheric pressure.