Which of the following new findings about strains of rats that do not normally reject liver transplants, if true, would support the authors' hypothesis? A. Stomach transplants are accepted by the recipients in all cases. B. Increasing the strength of the recipient's immune-response reaction can induce liver-transplant rejection. C. Organs from any other donor can be transplanted without rejection after liver transplantation. D. Preventing lymphocytes from being concentrated at the liver transplant produces acceptance of skin transplants.