This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T., Subject name: Radiology
[{'content': 'Bird beak sign on barium swallow is seen in? \nSelect and explain. \nA. Achlasia cardia, B. Carcinoma esophagus, C. Hiatus hernia, D. Nut cracker esophagus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' i.e., Achlasia cardia * "Bird beak appearance on barium study is seen in achlasia cardia.Important esophageal signs on radiographySignConditionRat tail appearance of esophagusEsophageal carcinomaMega-esophagus (sigmoid esophagus)"Bird beak" appearanceHurst phenomenonAchlasia cardiaYo-Yo motion of barium"Corkscrew" appearance (esophageal curling)Rosary-bead/sheikh kebab configurationChain of bead appearanceDiffuse esophageal spasm', 'role': 'assistant'}]