Answer:
A) having each person listen to just 1 song instead of 5.
Explanation:
Ravi could accurately use the outcome to compare the hearing capacities of his friends by this experiment if appropriate precautions are observed.
Playing 5 well known songs simultaneously could result to the interference of sounds when each participant moves away from the player. Which could naturally cause the variation in volume of the songs played with respect to the increasing distance.
Therefore, the reliability of the result from this experiment can be increased if each person listen to just 1 song instead of 5 at a predetermined volume. Each participant would be able to focus on hearing a song during the experiment.