This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gallbladder, Subject name: Surgery
Mirizzi's syndrome is: 
Select and explain. 
A. GB stone compressing common hepatic duct, B. GB carcinoma invading IVC, C. GB stone causing cholecystitis, D. Pancreatic carcinoma
A: GB stone compressing common hepatic duct
Answer: A: GB stone compressing common hepatic duct 
Explanation: Mirizzi's Syndrome (Functional Hepatic Syndrome) Obstruction of the common hepatic duct or CBD by external compression or by erosion of stone in the Hamann pouch or cystic duct