You are answering a USMLE-style medical question. Question: The only immunoglobulin found as a dimer has what primary function? Options: A) Protect against invasive helminth infection B) Protect against viral infections C) Inhibiting bacterial adherance and colonization of mucous membranes D) Provides the most specific recognition to circulating antigens in the bloodstream Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.