In immunology, how does an antibody identify an antigen among other substances in the body?

• A. The antibodies are coded genetically to match antigens.
• B. Antibodies attach randomly until they find matching antigens.
• C. Antibodies use cellular signals from T-cells for identification.
• D. By shape complementarity between the antigen's epitope and the antibody's paratope.

Answer: (D)