Letter d represents a wave's a)crest b)trough c)wave height d)wavelength

B) trough

Explanation:

A) Crest is the top or the highest point of the wave.

B) Trough is the bottom or the lowest part of the wave.

C) wave height is the vertical distance between the crest and the trough.

D) Wavelength is the distance between two successive wave crests or wave troughs.

Thus letter A represents wavelength, letter B represents wave height, letter C represents crest and letter D represents trough.

answer:

sequence 1- deletion

                  2- duplication

                  3- insertion

                  4- substitute

                  5- inversion