You are answering a USMLE-style medical question. Question: A 44-year-old man comes to the clinic because of a 6-month history of progressive fatigue. He has a history of intravenous heroin use. Physical examination shows scleral icterus. A serum study is positive for hepatitis C RNA. Therapy with interferon-α is initiated in combination with a second drug. The expected beneficial effect of the additional drug is most likely due to inhibition of which of the following enzymes? Options: A) Inosine monophosphate dehydrogenase B) DNA-dependent RNA polymerase C) DNA gyrase D) Dihydroorotate dehydrogenase Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.