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
Commonest cause of intestinal obstruction in down's syndrome – a) Colomic atresia b)  Intestinal atresiac) Duodenal atresia d)  Oesophageal atresia 
Select and explain. 
A. a, B. bc, C. ac, D. ad
B: bc
Answer: B: bc 
Explanation: Most common cause of Intestinal obstruction in Down's syndrome is duodenal atresia.
Duodenal atresia is a type of intestinal atresia.