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
What is more appropriate for diagnosis of CBD stones 
Select and explain. 
A. Ultrasonography, B. ERCP, C. O C G, D. IV cholangiography
B: ERCP
Answer: B: ERCP 
Explanation: USG is the first investigation
MRCP is the best non-invasive investigation
ERCP is the gold standard for diagnosing CBD stones. It has the advantage of providing a therapeutic option at the time of diagnosis.