The two main parts of a wave are the a. swell and whitecap. c. crest and trough. b. wavelength and wave height. d. rise and dip.  

Option C, Crest and Trough

Explanation:

A wave has two structural parts-  

a)Crest -  A crest is the lowermost part of the wave

b)Trough – A trough is the uppermost part of the wave

Wavelength in the horizontal distance between the mid points of two crests or two troughs while Wave height is the distance between the lowest and the highest point of a wave.

Thus, it is clear that crest and troughs are the essential units of construction of a wave while wave height and wavelength are the vertical and horizontal distances between the two wave components respectively.