This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Basic Concepts, Subject name: Pathology
[{'content': 'Which of the following is a pan-T lymphocyte marker? \nSelect and explain. \nA. CD 2, B. CD 3, C. CD 19, D. CD 25', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Antigen Designation Normal cellular distribution Primarily T-cell associated CD 1 Thymocytes and Langerhans cells CD3 Thymocytes, mature T cells CD4 Helper T cells, subset CD5 T cells and a small subset of B cells CD8 Cytotoxic T cells, subset of thymocytes, and some NK cells', 'role': 'assistant'}]