This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardio thoracic surgery  , Subject name: Surgery
[{'content': 'Retrocardiac lucency with air fluid level is seen in \nSelect and explain. \nA. Hiatus hernia, B. Distal end esophageal obstruction, C. Eventration of diaphragm, D. None', 'role': 'user'}, {'content': "Answer: A \nExplanation: Paraoesophageal hiatus hernia('Rolling hernia')may be visible on a plain radiograph of the chest as a gas bubble,often with a fluid level behind the hea.It is herniation of stomach fundus or rarely other abdominal contents through a hiatus,usually towards left side. Reference:Bailey & Love's sho practise of surgery,25 th edition,page no:1024;SRB's manual of surgery,5th edition,page no:795.", 'role': 'assistant'}]