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 among the following is not a beta lactamase inhibitor ? 
Select and explain. 
A. Sulbactam, B. Calvulanic acid, C. Piperacillin, D. None
C: Piperacillin
Answer: C: Piperacillin 
Explanation: None