Respuesta :

D. the trough part 
I can't really give an exact reason why, but if you look up a picture of a labeled standing wave then you will see that the highest point is a crest, and the lowest point is the trough. 

Answer:

Option (D)

Explanation:

The transverse wave travels in the form of crests and troughs.

The highest point on the wave is called crest.

The lowest point on the wave is called trough.