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: Microbiology
[{'content': 'The most common pathogens responsible for nosocomial pneumonias in the ICU are: \nSelect and explain. \nA. Gram positive organisms, B. Gram negative organisms, C. Mycoplasma, D. Virus infections', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]