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
A robust male baby with vigorous feeding and immediate vomiting at 2 months of age. Most probable diagnosis is: 
Select and explain. 
A. Paralytic ileus, B. Hirschsprung's disease, C. Brain tumor, D. Congenital hyperophic pyloric stenosis
D: Congenital hyperophic pyloric stenosis
Answer: D: Congenital hyperophic pyloric stenosis 
Explanation: Ans is 'd' i.e. Congenital hyperophic pyloric stenosis