You are answering a USMLE-style medical question. Question: A 64-year-old man with multiple sclerosis comes to the physician because of a 4-month history of urinary incontinence. The urge to urinate occurs suddenly, and he often is unable to make it to the bathroom before leaking urine. He has no incontinence with coughing or laughing. Digital rectal examination shows no abnormalities. Ultrasonography shows a normal post-void residual volume. Which of the following is the most appropriate pharmacotherapy for this patient's incontinence? Options: A) Midodrine B) Rivastigmine C) Mirtazapine D) Tolterodine Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.