The correct answer is A.
Blood type is determined by the presence or absence of two antigens, A and B, on the surface of red blood cells. People with blood type O have neither A nor B antigens on their red blood cells. People with blood type A have the A antigen, while people with blood type B have the B antigen. People with blood type AB have both A and B antigens.
If a person receives blood that contains antigens that they do not have, their immune system will attack the blood cells, which can be life-threatening. This is why it is important to receive blood that is compatible with your blood type.
Blood type is also important for blood donation. People with blood type O are considered universal donors because their blood can be given to people with any blood type. People with blood type AB are considered universal recipients because they can receive blood from people with any blood type.
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