The correct answer is A. the source should execute longitudinal vibrations.
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.
The production of sound requires the vibration of a source. The source of sound can be a solid, liquid, or gas. The vibration of the source causes the air molecules around it to vibrate. These vibrating air molecules then collide with other air molecules, causing them to vibrate as well. This process continues, with the sound waves traveling through the air until they reach our ears.
The type of vibration that produces sound is longitudinal vibration. Longitudinal vibrations are vibrations in which the particles of the medium move in the same direction as the wave. In the case of sound, the air molecules move back and forth in the direction that the sound wave is traveling.
Transverse vibrations are vibrations in which the particles of the medium move perpendicular to the direction of the wave. For example, when a guitar string vibrates, the string moves up and down, but the sound waves travel along the string in a horizontal direction.
The vibrations of the source are necessary to produce sound. If the source does not vibrate, then there will be no sound waves.