A- trough or crest
b- wavelength or frequency
c- level or equilibrium
d- trough or crest
e- amplitude or wavelength

need to figure out which is which.

A- Crest.

B- Wavelength.

C- Equilibrium.

D- Trough.

E- Amplitude.

Explanation: A crest is the point on a wave of maximum value of upward displacement within a cycle.  Wavelength is the distance between two identical adjacent points in a wave. Equilibrium is a state of balance between opposing forces; a state of balance in which opposing forces cancel one another. A trough is just the opposite of a crest, so it is the minimum(downward displacement) or lowest point of a wave in a cycle. Amplitude of a wave is the maximum distance or displacement moved by a point on a vibrating body or wave. Amplitude of a wave is directly proportional(∝) to the amplitude of the vibrating object(source).

Result: Crest, wavelength, equilibrium, trough and amplitude is the correct answer.

The correct answer would be b