Answer:
The correct answer is letter "E": influencer, gatekeeper, and decider.
Explanation:
As Mark's business is family-owned, it implies all the decisions are not made only by him. Then, in purchasing a food concession trailers he will have to let the other members of the family know about this decision.
Mark already decided Century Industries is the best option to take for the trailers but needs to influence his point of view to his family members. In other words, Mark will be the gatekeeper between his family business and Century Industries.