The movement of object affects sound. This was explained by the writer in the above given case with theory of Doppler Effect. The Doppler Effect is refers to a change in the frequency of radiation as it moves away/toward from the radiation. This effect produces a sudden change in pitch that is noticeable in a passing siren. In the above case, Doppler Effect is clearly explains why sound is heard more loudly and faintly once the object is moving away from the subject.
Therefore, as the oncoming sound waves approaching do possess high frequency and closeness of waves with higher amplitude in the above case. The ambulance is approaching with siren that causes higher frequency of sound waves due to Doppler Effect.
Thus, the options (d), (b) and (a) are incorrect.
Therefore, as the oncoming sound waves approaching do possess high frequency and closeness of waves with higher amplitude in the above case. The ambulance is approaching with siren that causes higher frequency of sound waves due to Doppler Effect.
Therefore, the correct option is – c. To inform the reader about how movement affects sound.