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
[{'content': 'Leflunomide used against Rheumatoid arthritis acts by inhibiting: \nSelect and explain. \nA. Ionisne monophosphate dehydrogenase, B. Dihydroorotate dehydrogenase, C. Aldehyde  dehydrogenase, D. TNF-α receptor', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Leflunomide inhibits Dihydroorotate Dehydrogenase and inhibits synthesis of pyrimidine and arrests growth of B-cells.', 'role': 'assistant'}]