The most popularly known blood grouping is the ABO grouping. It is named ABO and not ABC, because "O" in it refers to having :

Question

( A ) One antibody only-either anti-A and anti-B on the RBCs
( B ) Other antigens besides A and B on RBCs
( C ) No antigens A and B on RBCs
( D ) Overdominance of this type on the genes for A and B types