Monoclonal Antibody Specificity Steps:

• Monoclonal antibodies derive from one B-cell clone, producing identical molecules with uniform variable regions.
• Enzyme treatment (e.g., papain) separates variable (Fab) and constant (Fc) regions, but all Fab fragments retain the same antigen-binding site.
• Added to infected cells, variable regions bind virus antigens; since identical, they target the same epitope.
• Constant regions (Fc) alone do not bind antigens and lack opsonization signals for phagocytosis.

Why C is correct:

• Monoclonal antibodies bind one specific epitope by definition, so variable regions all attach to the same part (statement 2).

Why the others are wrong:

• A includes 1, false—soluble Fc fragments are not engulfed by phagocytes without antigen attachment.
• B includes 1 and 3, both false—Fc not phagocytosed, and variables bind same site, not different.
• D claims 3 only, false—monoclonal variables are uniform, unlike polyclonal antibodies.

Final answer: C