Ans.
A blood type or blood group of a person is determined by the antigen present on the surface of blood cell of that person. The antigen present on the cell surface may a carbohydrate, glycolipid, protein, or glycoprotein molecule. Humans show four blood groups, which are A, B, AB, and O on the basis of antigen present in their red blood cells.
Thus, the blank can be filled as 'antigens.'
