Answer: Hello there!
First, sound waves can propagate in any material, so options b and d can be discarded.
Sound waves propagate in spherical waves from the source, not in a perpendicular way, so this discards the option c.
Now, "sound waves have regions of compressions and refractions" is the right answer, these regions of compression and refraction are regions where the pressure changes, which is the thing that explains why sound waves are pressure waves.