To compare the hearing capacities of 5 of his friends, Ravi designs a simple experiment. He places a CD player at the end of a long hall containing a CD with 5 well-known songs. One by one each person hears the same 5 songs he plays softly but at a pre-determined volume.

Each person starts at a distance of 1 metre from the player and moves away from it. The distance at which a person says that he cannot hear the song any more, is noted. Others are not in the room when 1 person is hearing the songs.
Which of these steps may increase the reliability of the results obtained?

A)having each person listen to just 1 song instead of 5
B)allowing all people to stay in the room for the entire experiment
C)having each person start from far and walk towards the C
D )player Dvarying the volume for the different songs being played