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
Bird beak appearance of distal oesophagus is seen in: 
Select and explain. 
A. Achalasia cardia, B. Reflux oesophagitis, C. Carcinoma oesophagus, D. Hiatus hernia
A: Achalasia cardia
Answer: A: Achalasia cardia 
Explanation: Ans. Achalasia cardia