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: Surgery
[{'content': 'The diagnostic feature of congenital diaphragmatic hernia on prenatal ultrasonography is - \nSelect and explain. \nA. A cyst behind the left atrium, B. Mediastinal shift with normal hea axis, C. Peristalsis in the thoracic cavity, D. Absence of gas bubble under the diaphragm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. is \'c\' ie. Peristalsis in the thoracic cavity " The sonographic diagnosis of fetal CDH relies on the visualisation of abdominal organs in the chest. Other pointers may be absence of a normally positioned stomach, mediastinal displacement, small abdominal circumference and polyhydramnois."', 'role': 'assistant'}]