A 26 year old third_gravida mother delivered a male baby weighing 4-2 kg at 37 weeks of gestation through an emergency caesarean section, for obstructed labour. The child developed respiratory distress one hour after bih. He was kept nil per orally (NPO) and given intravenous fluids. He maintained oxygen saturation on room air. No antibiotics were given. Chest radiograph revealed fluid in interlobar fissure. Respiratory distress settled by 24 hours of life. What is the most likely diagnosis ?