Which of the formed elements of the blood determines abo blood types? a. white blood cells b. red blood cells c. antibodies d. plasma i know that the answer is either red blood cells or antibodies and i know this: red blood cells have special molecules called antigens on their surfaces. each person has either the a antigen, the b antigen, both the a and b antigens, or none of the antigens on their red blood cells. a person’s immune system will respond to these antigens by reacting with protein antibodies, which circulate in their blood plasma. but, i'm still not sure which is the correct answer.