Answer:
4) d
Explanation:
In the given figure, A is a wavelength which is the distance between two crests of a wave. B is a crest which is the highest point located on a wave at maximum distance upward from the middle of the wave. C is a trough which is an opposite of crest meaning that it is the lowest point on a wave from the middle.
Lastly, equilibrium is a point located in the middle of wave. In other words, it is the average of crests and troughs located on a wavelength.
