You are answering a USMLE-style medical question. Question: A 2-day-old boy delivered at 34 weeks gestation is found to have a murmur on routine exam. He is lying supine and is not cyanotic. He has a pulse of 195/min, and respirations of 59/min. He is found to have a nonradiating continuous machine-like murmur at the left upper sternal border. S1 and S2 are normal. The peripheral pulses are bounding. Assuming this patient has no other cardiovascular defects, what is the most appropriate treatment? Options: A) Indomethacin B) Thiazide diuretic C) Aspirin D) Penicillin Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.