D. Sound waves are being transmitted through the air in the drum.
Explanation:
Sound waves are being transmitted through the air in the drum because sound waves needs medium for their propagation from one place to another. Sound waves are considered as longitudinal waves due to parallel movement of air molecules to the velocity of the wave. The sound waves moves from one place to another through solid, liquid and gaseous medium. It moves fastest in solids but with lower speed in gases.
