Peter owns Big Bear Lodge. Because he needs cash, Peter borrows $50,000 from Catherine. In return, he grants Catherine one-half interest in Big Bear and the exclusive right to sell the lodge, which would enable her to recoup her loan. When Peter and Catherine have a personal falling out, Peter wishes to revoke their agency agreement but legally cannot because

A) of the duty of obedience

B) the loan achieved its purpose

C) it's an agency coupled with an interest

D) of agency at will