Answer: Point A is the answer for the potential energy. Point D is the answer for the kinetic energy.
Explanation:
The term is frequency.
The frequency is the number of vibrations per unit of time or the number of waves that passes a point per unit of time.
Every crest (and every trough) represents a pass of the wave so you can count the number of crests in an intervavl of time to find the frequency as the number of crests divided by the time elapsed.