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
Which of the following is not a risk factor for cholangiocarcinoma 
Select and explain. 
A. Thorotrast, B. Radon, C. Dioxin, D. Aflatoxin
D: Aflatoxin
Answer: D: Aflatoxin 
Explanation: Risk factors for cholangiocarcinoma Choledochal cyst Primary sclerosing cholangitis Ulcerative colitis. RPC or hepatolithiasis. Biliary enteric anastomosis HBV, HIV, HCV Choledocholithiasis Clonorchis sinensis and opisthorchis viverrini Cirrhosis Radon Asbestos, Nitrosamines, Dioxib(AND). Diabetes, Obesity, OCP's, smoking, Thorotrast, Isoniazid(DOSTI) Ref: Sabiston 20th edition Pgno :1514