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: Medicine
[{'content': 'The MOST sensitive test to diagnose GERD is: \nSelect and explain. \nA. 24 hour ambulatory pH monitoring, B. Upper GI endoscopy, C. Basal acid output measurement, D. Bernstein test', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Gastroesophageal Reflux Disease (GERD) Classic symptoms of gastroesophageal reflux are - water brash and substernal heaburn. Endoscopy is a sensitive test for diagnosis of esophagitis but will miss nonerosive reflux disease (NERD) MUST KNOW: The most sensitive test for diagnosis is 24-h ambulatory pH monitoring. Ref: Harrison, Edition-18, Page-2417.', 'role': 'assistant'}]