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 muscles."
B) "Yes,all human hearts are made of cardiac muscles,except some humans have different tissues inside their hearts and this could lead to a tissue rejection by the recipient."
C) "Yes,all human hearts are made of cardiac muscles.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 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."
E) "Yes,all human hearts are made of cardiac muscles.As far as the rejection issue,everyone has different MHC proteins on their tissues.Your aunt's immune system recognizes the 'self' tissues but can cause tissue rejection because of the 'nonself' tissue in her body having different MHC proteins."