Final answer:
The buying center is a concept in business-to-business marketing that identifies six roles involved in the purchasing process. The options given are all roles within this concept except for 'Buyer', which is not listed but is one of the six traditional buying center roles.
Step-by-step explanation:
The role question mentions are related to the buying center concept in organizational purchasing behavior.
The buying center is a part of the business-to-business marketing domain where multiple individuals within an organization are involved in the buying process, each playing different roles.
The traditional roles identified in a buying center include the Initiator, the Decider, the Influencer, the Buyer, the User, and the Gatekeeper.
Each of these individuals plays a distinct role in the purchase decision-making process, from recognizing the need for a product or service (Initiator) to actually authorizing the purchase (Decider).
Given the choices A. Initiator, B. Decider, C. User, and D. Influencer, all are recognized roles within the buying center framework except for 'Buyer', which is not listed amongst the options provided.
The 'Buyer' is the individual who handles the outsourcing and the actual procurement of goods and services.