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
A most common cause of nongonococcal septic arthritis is 
Select and explain. 
A. H.influenza, B. Staph-aureus, C. Pseudomonas, D. Streptococcus
B: Staph-aureus
Answer: B: Staph-aureus 
Explanation: Staphylococcus aureus is a Gram-positive, round-shaped bacterium that is a member of the Firmicutes, and it is a member of the normal flora of the body, frequently found in the nose, respiratory tract, and on the skin.