This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
[{'content': 'Gold standard investigation for Gastro-esophageal reflux disease is \nSelect and explain. \nA. Lower esophageal pH monitoring, B. Lower esophageal & pharyngeal pH monitoring, C. Endoscopic examination of esophagus, D. X-ray pharynx', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Answer- A. Lower esophageal pH monitoring24 Hour pH monitoring for reflux esophagitis24 hour pH monitoring (pH probe study), is the most sensitive test for diagnosis of gastroesophageal reflux. The test is performed by placing a catheter with a microelectrode that measures pH in the distal esophageal lumen for a duration of 24 hours. An episode of acid reflux usually is defined as an esophageal pH <4, for a duration greater than l5 - 20 seconds.', 'role': 'assistant'}]