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 on barium swallow study is seen in - 
Select and explain. 
A. Achlasia cardia, B. Carcinoma esophagus, C. Hiatus hernia, D. Diffuse esophageal spasm
A: Achlasia cardia
Answer: A: Achlasia cardia 
Explanation: ’’Bird beak appearance on barium study is seen in achalasia cardia.

             Important esophageal signs