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': 'Mononuclear phagocytes are produced by ? \nSelect and explain. \nA. Thymus, B. Spleen, C. Bone marrow, D. Liver', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Bone marrow Mononuclear macrophage cells originate in the bone marrow from precursor cells and become monocytes in about 6 days.", 'role': 'assistant'}]