At the PR Firm Where Gerald Works, Everyone Considers Him

At the PR firm where Gerald works, everyone considers him to be very good with his work and depends heavily on his knowledge to help the organization to solve its problems. Gerald is often seen teaching interns a simpler way to present an article, helping project managers with scheduling, and even the CEO often asks him for his opinion on important matter because of his experience and skill. Gerald's specialized knowledge depicts his ________.

A) legitimate power
B) coercive power
C) referent power
D) expert power
E) reward power