Answer:
STRING held by the man
Step-by-step explanation:
Wave is defined as a disturbance that travels through a MEDIUM and transfer energy from one point to another without causing any permanent displacement of the medium itself.
The medium through which wave travels varies e.g water, string, air etc
According to the diagram, wave travels through the string held by the man. This string is referred to as the MEDIUM through which the wave moves. The wave generated produces both crest (D) and trough (C) when displaced from its initial position (A)