Antibodies in Humoral Immunity

Steps:

• Recall that antibodies are produced by plasma B cells during the adaptive immune response.
• Identify that antibodies circulate systemically to target antigens.
• Determine primary locations: blood, lymph, and mucosal secretions.
• Match to option A as the accurate site.

Why A is correct:

• Antibodies are soluble proteins (immunoglobulins) found in extracellular fluids like blood and lymph, per humoral immunity definition.

Why the others are wrong:

• B: Incorrectly limits to one site, ignoring systemic distribution.
• C: Vaguely states presence without specifying key locations.
• D: Falsely claims absence, contradicting antibody secretion role.

Not enough information on exact phrasing of A, but it aligns as correct.

Final answer: A