Direct Coomb's test detects:
Answer is A (Antibodies attached to RBC Surface) Direct Coomb's test detects IgG Antibodies (or complements) attached to the surface of RBCs. Indirect Coomb's test detects IgG antibodies in the serum (e.g. Anti-D Antibodies).
Antibodies attached to RBC Surface
Antibodies in the serum
Antigens attached to RBC Surface
Antigens in the serum