B. This defines the principal broker, who has ultimate legal and operational responsibility for the entire firm, not a supervising broker who oversees a specific part of it.
C. This describes a non-affiliated or cooperating broker in a transaction, which is an external role and not a supervisory position within a brokerage firm.
D. This describes an associate broker who is not acting in a supervisory capacity. A supervising broker, by definition, has licensees assigned to them for oversight.