This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
[{'content': 'Immunoglobulin secreted by fetus as primary response - \nSelect and explain. \nA. IgA, B. IgM, C. IgG, D. IgD', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., IgM", 'role': 'assistant'}]