John, an artist, asks his artist friend Tina to take some of his paintings to an art fair w/ her, and to sell them for him. The fact that John and Tina never discussed whether John would pay her for this service proves that:

(A) Their relationship is not an agency.
(B) Their relationship may be an agency, but if so it is "at will." 9
(C) Their relationship may be an agency, but it is an independent contractor relationship.
(D) If anything, that artists are cheap.