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': 'Which of the following test differentiates between diffuse esophageal spasm and GERD \nSelect and explain. \nA. Barium swallow, B. Manometry, C. Ambulatory 24 hour pH monitoring, D. Biopsy', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Symptoms and manometric findings of diffuse esophageal spasm can be caused by GERD. To differentiate between them it is mandatory to do 24 hour pH monitoring.', 'role': 'assistant'}]