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
Most common ASD in down syndrome is ? 
Select and explain. 
A. Ostium primum, B. Ostium secondum, C. Absent atrial septum, D. Sinus venosum
A: Ostium primum
Answer: A: Ostium primum 
Explanation: Ans. is 'a' i.e., Ostium primum