Answer: The correct answer is "equilibrium to the crest and is called the amplitude".
Step-by-step explanation:
Amplitude is the maximum displacement of the particle from its equilibrium position in the vertical direction.
The wavelength is the distance between the two consecutive troughs or crests. But it is in horizontal direction.
Frequency is the number of waves that pass in a given time form a fixed point.
Therefore, the vertical displacement of the wave is measured from the equilibrium to the crest and is called the amplitude.