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: Medicine
[{'content': 'Which 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: None', 'role': 'assistant'}]