C . Cochlear nerve degeneration is not a cause of conduction deafness. However, it may be the cause of sensorineural deafness.
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Conductive deafness occurs when something interferes with the sound conduction to internal ear. It may be caused by impacted cerumen ( ear wax) in external auditory canal, by otosclerosis or otitis media. Otitis media is infection in the middle ear; otosclerosis may caused by fusion of the ossicles to one another or by the base of the stapes being fused to the oval window. An additional cause of conduction deafness is rupture of the ear drum. In a case of otosclerosis, sound is transmitted largely by skull bones. Sensorineural deafness occurs when neural structures are damaged.