This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
[{'content': 'The lineage-specific marker for B cells is \nSelect and explain. \nA. CD 19, B. CD 20, C. CD 21, D. CD 22', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Lineage-specific B cell marker is CD 19. However, on IHC the best marker is CD 20. CD 21 is the receptor for EBV. Ref: Ananthanarayana textbook of Microbiology 9th edition Pgno : 136', 'role': 'assistant'}]