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 of the following drug is not used against Pseudomonas ? 
Select and explain. 
A. Piperacillin, B. Carbenicillin, C. Ticarcillin, D. Oxacillin
D: Oxacillin
Answer: D: Oxacillin 
Explanation: None