The correct option is D Vestibular apparatus ensures that we maintain our body balance.
Pinna collects the sound waves from the environment and conducts it through the external auditory canal towards the eardrum. The eustachian tube equalizes air pressure inside the ear to match the normal air pressure allowing the sound to vibrate freely. This vibration causes the fluid inside the cochlea to vibrate. Due to which the sensory hair cells are stimulated. They generate auditory impulses which are transmitted to the brain by the auditory nerves. Apart from hearing, our ears ensure that we maintain our body balance with the help of vestibular apparatus.