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 B lymphocyte.marker - \nSelect and explain. \nA. CD 19, B. CD 5, C. CD 10, D. CD 38', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]