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 one of the following is a pan T lymphocyte marker - \nSelect and explain. \nA. CD2, B. CD3, C. CD19, D. CD25', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The most clearcut differentiation between T and B cells is by their surface markers, for example, by demonstration of CD3 on T cells and Ig on B cells.', 'role': 'assistant'}]