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: Medicine
All of the following are known predesposing factors for cholangiocarcinoma except : 
Select and explain. 
A. CBD stones, B. Clonorchis sinensis, C. Ulcerative colitis, D. Primary sclerosing cholangitis
A: CBD stones
Answer: A: CBD stones 
Explanation: Answer is A (CBD stone) : Cholelithiasis is not clearly a predisposing factor for Cholangiocarcinoma - Harrison The predisposing factors of cholangiocarcinoma include : I. Chronic hepato-biliary parasite infection (Clonorchiasis or Asiatic cholangio-hepatitis) Q Congenital Anomaly with ectatic ducts (Choledochal cyst).Q Sclerosing cholangitis Q Ulcerative colitis Occupational exposure to carcinogensQ(Rubber + Automotive plants) Note: Nodular lesions that arise at the bifitrcation of hepatic ducts are called Klastskin tumors. Q