This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
[{'content': 'Most common gram-negative organism in cystic fibrosis is \nSelect and explain. \nA. Pseudomonas, B. Escherichia coli, C. Klebsiella, D. Legionella', 'role': 'user'}, {'content': 'Answer: A \nExplanation: It occurs in patients with underlying conditions such as cystic fibrosis specially in the Caucasian population', 'role': 'assistant'}]