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 of the following have beta lactam ring except : 
Select and explain. 
A. Penicillin, B. Linezolid, C. Cefotaxime, D. Imipenem
B: Linezolid
Answer: B: Linezolid 
Explanation: None