A sound producing body is at considerable distance from a man. There can be four different media W, X, Y and Z between the sound producing body and the man. The medium X brings the sound to man most quickly whereas medium Z tajes the maximum time. The time taken by medium W in bringing sound to man is less than that of X but more than that of Z. The medium Y, however, fails to bring the sound from the sound producing body to the man. Which medium could be the one:

(a) having no fixed shape and no fixed volume?

(b) having a fixed volume but no fixed shape?

(c) having the same composition as that on the moon?

(d) having a fixed shape and a fixed volume?