A Friend Tells You the Following Story

A friend tells you the following story. "My aunt just received a heart transplant. Her doctors warned us that her body might reject the tissue. I just can't understand how that could happen as human hearts are made of the same tissues, aren't they?" How do you respond?

A) "Yes, all human hearts are made of cardiac muscle. But, most people have different MHC class I proteins on their cell surfaces. Your aunt's immune system can cause tissue rejection because of the 'nonself' MHC proteins on the donor heart."
B) "Yes, all human hearts are made of cardiac muscle, so I am as perplexed as you are."
C) "Yes, all human hearts are made of cardiac muscle. As far as the rejection of tissues goes, your aunt might have different antibodies than did the donor, which could lead to a rejection."
D) "Yes, all human hearts are primarily made of cardiac musclec, except some humans have different tissues inside their hearts and this could lead to a tissue rejection by the recipient."
E) "Yes, all human hearts are made of cardiac muscles. However, your aunt might have been given some type of drug during the transplant operation that might cause tissue rejection. You can never be too careful in a hospital, you know."