Patient 1 and patient 2 both had a transplant. which explains why patient 1 had a successful transplant and patient 2 did not?
a. patient 1 underwent tissue typing, but patient 2 was tested for antigen compatibility.
b. patient 1 underwent long-term immunosuppressive therapy, but patient 2 was given immunosuppressants during the surgery.
c. patient 1 began an exercise routine after surgery and maintained it for the rest of his life, but patient 2 led a more sedentary lifestyle.
d. patient 1 followed a healthy diet low in salt and fat, but patient 2 did not monitor his diet.

The correct answer is option B. Patient 1 underwent long-term immunosuppressive therapy, but patient 2 was given immunosuppressants during the surgery.

Whenever organ transplantation occurs, if the patient is not closely related to the donor then patient's body tends to reject the donated the organ. This is known as graft rejection. It occurs when MHC of the host and the donor doesn't match by 50% or more. As a result of this, the host's body considers the donated organ as foreign and generates very strong immune response against the transplanted organ. It causes foreign tissue lysis and leads to internal bleeding. In order to avoid this situation, the patients are given immunosupressant drugs for a very long time. After treating them with these drugs gradually body starts to adapt the foreign organ which leads to successful transplant even if the MHC doesn't match by 50%. The patient 1 underwent long term immunosupressive therapy so transplant was successful. But, in case of patient 2 the drug treatment was for a very short period of time so his body couldn't adapt the foreign organ leading to transplant failure.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.