You are answering a USMLE-style medical question. Question: A 35-year-old man visits your office for his annual health checkup. He was diagnosed with generalized anxiety disorder 6 months ago, which is being treated with citalopram. He comments that his symptoms have improved since initiating the prescribed therapy; however, in the past 2 months, he has been unable to have sexual intercourse due to weak tumescence and low libido. His blood pressure is 122/74 mm Hg, heart rate is 75/min, and respiratory rate is 16/min. Physical examination reveals regular heart and lung sounds. What is the appropriate step in the management of this patient? Options: A) Lowering citalopram dose B) Addition of bupropion C) Switch to fluoxetine D) Switch to selegiline Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.