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 for reflux esophagitis is - \nSelect and explain. \nA. Manometry, B. Barium swallow, C. 24 hours pH study, D. X-ray abdomen', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]