I believe it is A. Just don't hold me down on that. :D
The answer is longitudinal. There are two types of waves: transverse and longitudinal. Transverse waves are those whose vibrations are perpendicular to the direction of the wave. Longitudinal or compression waves are those whose vibrations are in the same direction as the wave. Sound is caused by the compression of vibrations of molecules.
A device used to initiate and control a sustained nuclear chain reaction.
The Sun is the world's main source of energy. Without it we would not be able to live.