Final answer:
Individual particles of a medium in a surface wave move in a circular motion that is perpendicular to the energy propagation direction. In transverse waves specifically, this movement is strictly up and down and perpendicular to the wave's travel path.
Step-by-step explanation:
In a surface wave, individual particles of the medium move in a circular motion as the energy of the surface wave passes through them. The correct answer to the student's question is B) perpendicular. This is because in a surface wave, particles make a circular path combining movement parallel and perpendicular to the direction of wave propagation, like the ripples on water. However, in a transverse wave specifically, particles of the medium move perpendicular to the direction of the wave motion. When a transverse wave is traveling from left to right, the particles of the medium oscillate up and down, which is perpendicular to the wave's direction of travel. This creates the distinctive peaks (crests) and valleys (troughs) seen in diagrams of transverse waves.