In an Effort to Get His Students to Practice Frequently

In an effort to get his students to practice frequently, a vocal coach hangs posters of their favorite singers and bands on the wall.Underneath each, he writes the numbers of hours they practiced on average and how many years it took them to "get to the top." He is relying on

A) Legitimate power
B) Emotional appeal
C) Referent power
D) Direct display of authority