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
All have beta lactam ring EXCEPT - 
Select and explain. 
A. Penicillin, B. Linezolid, C. Cefotaxime, D. Imipenem
B: Linezolid
Answer: B: Linezolid 
Explanation: 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).