This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Esophagus, Subject name: Surgery
[{'content': 'The gold standard for diagnosis of gastroesophageal reflux disease (GERD) is: \nSelect and explain. \nA. Barium swallow, B. Endoscopy, C. 24-hours pH monitoring, D. Esophageal manometry', 'role': 'user'}, {'content': "Answer: C \nExplanation: Barium swallow- IOC for diagnosis of Hiatus hernia and Zenker's diveicula Endoscopy + Biopsy- IOC for diagnosis of Barret's esophagus 24 hours PH monitoring- Gold standard Investigation for GERD Esophageal manometry- IOC for diagnosis of motility disorders of esophagus like Achalasia cardia, Diffuse esophageal spasm and Nut cracker's esophagus.", 'role': 'assistant'}]