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': 'Which one of the following immunoglobulins constitues the antigen binding component of B-cell receptor - \nSelect and explain. \nA. IgA, B. IgD, C. IgM, D. IgG', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The BCR is composed of surface-bound IgD or IgM antibodies and associated Ig-a and Ig-b heterodimers, which are capable of signal transduction Reff: www.mayoclinic.com', 'role': 'assistant'}]