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: Physiology
[{'content': 'Primary sites of lymphocyte production are \nSelect and explain. \nA. Bone marrow and Thymus, B. Spleen and Lymph nodes, C. Lymph nodes and mucosa associated lymphoid tissue, D. Spleen and mucosa associated lymphoid tissue', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]