Final answer:
Personal selling (option B) is identified as a key component of a firm's promotional mix because it involves direct interaction with potential and existing customers, allowing personalized communication and long-term relationship building.
Step-by-step explanation:
The question asks which option is a useful vehicle for communication with present and potential buyers, making it part of a firm's promotional mix. The correct answer is B. personal selling. Personal selling is the direct interaction between a sales representative and a prospective or existing customer with the intention to make a sale or maintain a relationship.
It is an important component of a firm's promotional mix, which also includes advertising, sales promotion, public relations, and direct marketing. Personal selling allows for personal communication and feedback, tailoring the message to the individual customer's needs, and building long-term customer relationships.