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: Radiology
Best investigation for diagnosis of ampullary gall stone with obstructive jaundice is: 
Select and explain. 
A. Intravenous cholecystography, B. OCG, C. PTC, D. ERCP
D: ERCP
Answer: D: ERCP 
Explanation: Ans. ERCP