This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Anatomy
Best investigation modality for gallbladder 
Select and explain. 
A. OCG, B. PTC, C. Ultrasound, D. Intravenous cholangiogram
C: Ultrasound
Answer: C: Ultrasound 
Explanation: USG is the investigation of choice for Calculous cholecystitis Chronic cholecystitis Cholelithiasis Ref: Sabiston 20th edition Pgno : 1487