<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 4-month-old girl is brought to the physician because she has been regurgitating and vomiting 1015 minutes after feeding for the past 3 weeks. She is breastfed and formula-fed. She was born at 38 weeks gestation and weighed 2966 g 6 lb 9 oz. She currently weighs 5878 g 12 lb 15 oz. She appears healthy. Vital signs are within normal limits. Examination shows a soft and nontender abdomen and no organomegaly. Which of the following is the most appropriate next best step in management?? A: Esophageal pH monitoring, B: Upper endoscopy, C: Ultrasound of the abdomen, D: Pantoprazole therapy, E: Positioning therapy,  <response>: This is a clinical vignette about a 4-month-old infant girl with a 3 week history of regurgitation and vomiting after feeding. She was born at 38 weeks gestation and has had appropriate weight gain. She appears healthy on exam. The key findings are:- 4 month old infant - Regurgitation and vomiting after feeds for 3 weeks- Born at 38 weeks gestation - Appropriate weight gain - Healthy appearance and normal vital signs and abdominal examThis presentation is most consistent with uncomplicated infantile gastroesophageal reflux, which is common in infants. The next step in management would be a trial of conservative measures such as feeding changes, positioning therapy, andor a trial of an acid-reducing medication like a proton pump inhibitor. More invasive or costly tests like endoscopy, pH monitoring, or imaging are not indicated as first-line tests in an otherwise healthy infant.E: Positioning therapy 