When Dr Zane Greene's Staff Complained About How Slow His Autoclave

When Dr. Zane Greene's staff complained about how slow his autoclave is when they use it to sterilize dental equipment, he made a couple of phone calls and then ordered the new Vela autoclave because it is the fastest and safest on the market. In terms of the buying-decision process, Dr. Greene assumed the roles of:

A) gatekeeper, decider, and buyer.
B) user, influencer, decider, and buyer.
C) influencer and gatekeeper.
D) decider, and buyer.
E) influencer, decider, and gatekeeper.