This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immune system, Subject name: Medicine
[{'content': 'Extra - aicular manifestations of RA are all except \nSelect and explain. \nA. Rheumatoid nodule, B. Pericarditis, C. Spleen atrophy, D. Osteoporosis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ref - Davidsons 23e p1024', 'role': 'assistant'}]