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
Which is not a beta lactam antibiotic ? 
Select and explain. 
A. Penicillin, B. Carbepenem, C. Monobactam, D. Azithromycin
D: Azithromycin
Answer: D: Azithromycin 
Explanation: None