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': 'Gram staining of the sputum of the patients with pneumonia is diagnostic with all these pathogens, EXCEPT: \nSelect and explain. \nA. S. pneumoniae, B. S. aureus, C. Gram-negative bacteria, D. Coxiella burnetii', 'role': 'user'}, {'content': "Answer: D \nExplanation: Gram's staining may identify ceain pathogens (e.g., S. pneumoniae, S. aureus, and gram-negative bacteria) by their characteristic appearance. A sputum sample must have 1. >25 neutrophils 2. <10 squamous epithelial cells per low-power field, to be adequate for culture. Ref: Harrison, E-18, P-2133", 'role': 'assistant'}]