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
Which one of the following immunoglobulins constitues the antigen binding component of B-cell receptor - 
Select and explain. 
A. IgA, B. IgD, C. IgM, D. IgG
B: IgD
Answer: B: IgD 
Explanation: 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