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': 'Nosocomial pneumonia is most commonly caused by- \nSelect and explain. \nA. Gram -ve bacilli, B. Gram + ve bacilli, C. Gram - ye cocci, D. Mycoplasma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]