<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 10-day-old male infant is brought to the emergency room for abdominal distension for the past day. His mother reports that he has been refusing feeds for about 1 day and appears more lethargic than usual. While changing his diaper today, she noticed that the baby felt warm. He has about 1-2 wet diapers a day and has 1-2 seedy stools a day. The mother reports an uncomplicated vaginal delivery. His past medical history is significant for moderate respiratory distress following birth that has since resolved. His temperature is 101F 38.3C, blood pressure is 9869 mmHg, pulse is 174min, respirations are 47min, and oxygen saturation is 99 on room air. A physical examination demonstrates a baby in moderate distress with abdominal distension. What is the best initial step in the management of this patient?? A: Cystoscopy, B: Radionuclide scan, C: Renal ultrasound, D: Urinary catheterization, E: Voiding cystourethrogram,  <response>: This is a case of a 10-day-old infant presenting with abdominal distension, fever, decreased urine output, and lethargy. The key findings are abdominal distension, fever, and decreased urine output in a newborn. The differential diagnosis includes intestinal obstruction, necrotizing enterocolitis, and urinary tract infectionobstruction. However, before ordering imaging studies, the initial step should be to stabilize the patient. In a newborn with fever, respiratory distress, and signs of dehydration, the best initial step is urinary catheterization to monitor urine output and guide fluid resuscitation.D: Urinary catheterization 