Correct Answer:
C. down
The correct answer is down. The phrasal verb 'turn down' means to reduce the volume, intensity, or strength of something. The context 'I am getting deaf' clearly indicates a need to decrease the volume of the music.
- with: 'With the volume' does not form a coherent phrasal verb in this context and is grammatically incorrect.
- for: 'For the volume' is grammatically incorrect and does not convey the intended meaning of reducing the volume.
- behind: 'Behind the volume' makes no logical sense in this sentence and is grammatically incorrect.