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Three hours after delivery, a 1800-g (3-lb 15-oz) male newborn develops respiratory distress. He was born at 31 weeks' gestation to a 27-year-old primigravid woman. His temperature is 36.9°C (98.4F), pulse is 140/min, respirations are 69/min, and blood pressure is 60/30 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 92%. Examination shows nasal flaring and expiratory grunting. An x-ray of the chest is shown. Which of the following is the most likely cause of these findings?