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': 'Not a Radiological feature of achalasia cardia \nSelect and explain. \nA. Megaesophagus, B. Bird beak appearance, C. Rat tailed appearance, D. Antral nipple sign', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Antral nipple sign - Feature of Congenital hypertrophic pyloric Stenosis.', 'role': 'assistant'}]