Karen Asked Her Co-Worker, "Why Does Larry Always Consult with David

Karen asked her co-worker, "Why does Larry always consult with David before making any major business decisions? David is 65 years old. He's very quiet and unassuming. He's been working here for over 40 years and isn't even in a management position." Ben replied, "David voluntarily stepped down from management roles 15 years ago. He decided that management was not his strength nor his passion, but rather technical work was. He is an incredibly important person, and leader, within our organization." Karen asked, "But why?" Ben responded,

A) "David has referent power, with personal characteristics that appeal to others."
B) "David has legitimate authority via chain of command."
C) "David is a charismatic leader, having a dominant personality."
D) "David has expertise and knowledge that others believe in, can learn from, and can gain from."
E) "David has supervisory leadership abilities that he exercises on a regular basis."