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': 'The accurate method of diagnosis of gastroesophageal reflux disease (GORD) is - \nSelect and explain. \nA. Barium swallow, B. Endoscopy, C. 24 hour pH monitoring, D. Oesophageal manometry', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]