This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
[{'content': 'The gold standard for diagnosis of gastroesophageal reflux disease (GERD) is \nSelect and explain. \nA. Endoscopy, B. Barium swallow, C. Esophageal manometry, D. 24-hours ambulatory pH monitoring', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The most sensitive test for diagnosis of GERD is 24-h ambulatory pH monitoringRef: Harrison; 19th edition; Page no: 1894', 'role': 'assistant'}]