This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
[{'content': 'All are peripheral lymphoid organs except - \nSelect and explain. \nA. Lymph nodes, B. Spleen, C. Mucosa associated lymphoid tissue, D. Thymus', 'role': 'user'}, {'content': "Answer: D \nExplanation: Thymus & bone marrow are primary/central lymphoid organ, the spleen & lymph nodes are the secondary/peripheral lymphoid organ Reff: Ananthanarayanan & Paniker's textbook of microbiology 9th edition pg: 128", 'role': 'assistant'}]