You are answering a USMLE-style medical question. Question: A 65-year old man presents with gradually worsening rigidity of his arms and legs and slowness in performing tasks. He says he has also noticed hand tremors, which increase at rest and decrease with focused movements. On examination, the patient does not swing his arms while walking and has a shortened, shuffling gait. An antiviral drug is prescribed which alleviates the patient’s symptoms. Which of the following drugs was most likely prescribed to this patient? Options: A) Amantadine B) Ribavirin C) Levodopa D) Zidovudine Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.