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: Radiology
[{'content': 'Investigation of choice in diffuse esophageal spasm is \nSelect and explain. \nA. Manometry, B. Esophagoscopy, C. Barium examination showing tertiary contractions, D. CT thorax', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Investigation of choice for motor disorders (including diffuse esophageal spasm) is esophageal manometry.', 'role': 'assistant'}]