State three conditions necessary for sound to be heard.

(N/A) $(i)$ There must be a vibrating body capable of transferring its energy to its surroundings.
$(ii)$ There must be a material medium to pick up the energy and propagate it in the forward direction.
$(iii)$ There must be a receiver,such as the human ear,to receive the sound vibrations and transmit them to the brain for final interpretation.