Answer:
A. compressions; rarefactions
Step-by-step explanation:
As we know that we have two type of travelling wave as per propagation of wave
1) Transverse wave
2) Longitudinal wave
In transverse waves we know that medium particles will move to and from in perpendicular direction of propagation of wave
while in case of longitudinal wave we know that particles will move to and fro in the direction of propagation of wave itself
so here correct answer will be
A. compressions; rarefactions