This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gall Bladder & Bile Ducts, Subject name: Surgery
Investigation of choice in gall bladder stone is: 
Select and explain. 
A. USG, B. X-ray abdomen, C. OCG, D. Intravenous cholangiography
A: USG
Answer: A: USG 
Explanation: Ans: a (USG)Ref: Bailey & Love, 24th ed, p. 1097 & 23rd ed, p. 968