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: Medicine
[{'content': 'Causative agent for rheumatoid ahritis is: \nSelect and explain. \nA. Mycoplasma, B. Mycobacaterium avium, C. Yersinia, D. Herpes virus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Answer is A (Mycoplasma) The true causative agent for Rheumatoid ahritis is not known. Mycoplasma has been suggested as a possible causative agent, and hence is the single best answer of choice', 'role': 'assistant'}]