This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'Which of the following immunoglobulin is a pentamer? \nSelect and explain. \nA. IgG, B. IgA, C. IgM, D. IgD', 'role': 'user'}, {'content': 'Answer: C \nExplanation: IgM Both secretory IgA (dimeric) and IgM (pentameric) have J chains IgM is the main immunoglobulin produced early in the primary immune response. IgM is present on the surface of viually all uncommitted B cells. It is a pentamer composed of five H,L, units (each similar to one IgG unit) and one molecule of J (joining) chain.', 'role': 'assistant'}]