The correct option is A Basilar
The basilar membrane is the base for the sensory cells of hearing, the hair cells that contain stereocilia. There are approximately 15,000 hair cells in each human ear. They function as the base of the sensory cells. Due to its location, the basilar membrane places the hair cells in a position where they are adjacent to both the endolymph and the perilymph which is a precondition of hair cell function.