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: Orthopaedics
[{'content': 'A most common cause of nongonococcal septic arthritis is \nSelect and explain. \nA. H.influenza, B. Staph-aureus, C. Pseudomonas, D. Streptococcus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Staphylococcus aureus is a Gram-positive, round-shaped bacterium that is a member of the Firmicutes,\xa0and it is a member of the normal flora of the body, frequently found in the nose, respiratory tract, and on the skin.', 'role': 'assistant'}]