Which of the following is a part of a wave?
a. crest
c. trough
b. drift
d. both a and c

Crest and trough

Explanation:

The disturbance created in a medium is called a wave. The particles of wave transfers energy from one point to another. The topmost part of a wave is called the crest while the lowermost part of the wave is called the trough.

A wave is characterized by its amplitude, wavelength, frequency, time period etc.

The distance between two consecutive crests or troughs is called the wavelength of a wave. The number of oscillations produced per second is called the frequency of the wave.

Hence, the crest and the trough are the part of a wave. So, (d) is the correct option.