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
One of the following is not penicillinase susceptible: 
Select and explain. 
A. Amoxicillin, B. Penicillin G, C. Piperacillin, D. Cloxacillin
D: Cloxacillin
Answer: D: Cloxacillin 
Explanation: None