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: Pediatrics
[{'content': 'Most common ASD in down syndrome is ? \nSelect and explain. \nA. Ostium primum, B. Ostium secondum, C. Absent atrial septum, D. Sinus venosum', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Ostium primum", 'role': 'assistant'}]