Concept:Audio aids are learning tools that convey information through the sense of hearing.
Explanation:Audio aids work by activating the auditory system of the learner.
A gramophone is used to play previously recorded sounds, so it is classified as an audio aid.
Radio, linguaphone, and tape recorder are other common examples of audio aids.
The remaining options—O.H.P., Epidiascope, and Magic Lantern—are projective aids.
Projective aids are audio-visual aids that display concepts on a screen using both sight and sound.
Therefore, among the given options, only the gramophone qualifies as a pure audio aid.
Answer:C. Gramophone