I believe the correct answer is the presence of antigens.
Step-by-step explanation:
Red blood cells have specific antigens on their surface that determine the blood group are hereditable. For example, blood group A means the person has the A antigen, B means the B antigen and AB means the person has both A and B antigens. The other group is blood group O and that means the person lacks the antigens to to make a particular blood group. The human body produces other chemicals called antibodies that attacks antigens and that is why you can only recieve a blood group that is yours to prevent the antibodies from attacking you. Since there are only 2 antigens, a person with antigen A produces antibodies against the rival antigen B. In the case of blood group AB where a person has both antigens, the body lacks all the antibodies in order to prevent the body from attacking itself. So a person with blood group AB lacks antigens a and b.This means the person can receive blood from any blood group since there are no antibodies to attack any antigen. They however can only donate to a person who has the same AB bloodgroup since all the other blood groups have antibodies against antigens and adding blood that has antigens will cause a severe blood transfusion reaction.