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: Pharmacology
[{'content': 'Pseudomonas is resistant to - \nSelect and explain. \nA. Vancomycin, B. Aztreonam, C. Ciprofloxacin, D. Polymyxin B', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Vancomycin o Vancomycin is NOT active against pseudomonas.", 'role': 'assistant'}]