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: Medicine
[{'content': 'The most sensitive diagnostic evaluation for achalasia cardia is: \nSelect and explain. \nA. Barium swallow, B. Esophageal manometry, C. Upper GI endoscopy, D. Chest X - Ray', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Achalasia is diagnosed by barium swallow x-ray, esophageal manometry and rarely with endosc (To exclude pseudoachalasia). The diagnostic criteria for achalasia with esophageal manometry are impaired LES relaxation and absent peristalsis. High-resolution manometry identifies early disease before esophageal dilatation and food retention, it is the most sensitive diagnostic test. Ref: Harrison, Edition-18, Page-2431', 'role': 'assistant'}]