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
Allopurinol potentiates the action of : 
Select and explain. 
A. Corticosteroids, B. Probenecid, C. 6–Mercaptopurine, D. Ampicillin
C: 6–Mercaptopurine
Answer: C: 6–Mercaptopurine 
Explanation: None