The correct option is A Both A and R are true and R is the correct explanation of A
Organ transplantation is the transfer of an organ from a donor to a recipient.
The transplanted organ is a foreign substance to the recipient body. These organs have molecules that act as antigens and activate specific immune responses. Hence, immune response is elicited by the body of the recipient against the new organ, thereby, destroying the organ. This is known as graft rejection.
To avoid this, the immune system of the host/recipient is suppressed with the help of immunosuppressive agents/drugs.