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': 'Bird beak appearance of distal oesophagus is seen in: \nSelect and explain. \nA. Achalasia cardia, B. Reflux oesophagitis, C. Carcinoma oesophagus, D. Hiatus hernia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Achalasia cardia', 'role': 'assistant'}]