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
Leflunomide used against Rheumatoid arthritis acts by inhibiting: 
Select and explain. 
A. Ionisne monophosphate dehydrogenase, B. Dihydroorotate dehydrogenase, C. Aldehyde  dehydrogenase, D. TNF-α receptor
B: Dihydroorotate dehydrogenase
Answer: B: Dihydroorotate dehydrogenase 
Explanation: Leflunomide inhibits Dihydroorotate Dehydrogenase and inhibits synthesis of pyrimidine and arrests growth of B-cells.