Final answer:
Longitudinal waves are waves in which the particles of the medium vibrate parallel to the direction of the wave propagation, causing compression and rarefaction of the medium.
Step-by-step explanation:
The waves that are also known as push-pull waves are longitudinal waves (option a).
Longitudinal waves are waves in which the particles of the medium vibrate parallel to the direction of the wave propagation. The wave motion causes compression and rarefaction of the medium, giving rise to the push-pull motion.