This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pharmacology
[{'content': 'The gold standard for diagnosis of gastroesophageal reflux disease (GERD) is not related-surgery \nSelect and explain. \nA. Endoscopy, B. Barium swallow, C. Esophageal manometry, D. 24-hours pH monitoring', 'role': 'user'}, {'content': 'Answer: D \nExplanation: .', 'role': 'assistant'}]