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': 'Most common organism causing ventilator associated pneumonia - \nSelect and explain. \nA. Legionella, B. Pneumococcus, C. Pseudomonas, D. Coagulase negative staphylococcus', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]