You are answering a USMLE-style medical question. Question: A male newborn is evaluated 24 hours after delivery for high-pitched crying, poor feeding, rhinorrhea, and low-grade fever. He was born at 40 weeks' gestation at 2514 g (5.54 lb) to a 28-year-old woman, gravida 3, para 2, by an uncomplicated cesarean section. Apgar scores were 8 and 9 at 1 and 5 minutes, respectively. The mother did not receive prenatal care. The infant's temperature is 38.0°C (100.4°F), pulse is 170/min, and blood pressure is 71/39 mm Hg. Examination shows hyperreflexia, tremors, and an excessive startle response. These symptoms are mostly like due to maternal use of which of the following? Options: A) Mu receptor agonist B) Nicotinic acetylcholine receptor agonist C) Monoamine reuptake antagonist D) Thyroperoxidase inhibitor Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.