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: Pathology
[{'content': 'Pre-B cells and B cells are produced in ? \nSelect and explain. \nA. Bone marrow, B. Thymus, C. Tonsils, D. Gut associated lymphoid tissue', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Bone marrow", 'role': 'assistant'}]