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': 'All have beta lactam ring EXCEPT - \nSelect and explain. \nA. Penicillin, B. Linezolid, C. Cefotaxime, D. Imipenem', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Linezolid beta-lactam antibiotics contain beta-lactam ring. These are penicillins, cephalosporins (e.g. cefotoxime), monobactams (aztreonam) and carbapenems (imipenem, meropenem).", 'role': 'assistant'}]