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': 'Beta lactam antibiotics are all except - \nSelect and explain. \nA. Amoxicillin, B. Aztreonam, C. Ceftriaxone, D. Vancomycin', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., Vancomycin", 'role': 'assistant'}]