This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
The organism causing biliary duct obstruction? 
Select and explain. 
A. Clonorchis sinensis, B. Ankylostoma duodenale, C. Strongyloides stercoralis, D. Enterobius vermicularis
A: Clonorchis sinensis
Answer: A: Clonorchis sinensis 
Explanation: Hepatobiliary ParasitismCommon in Southern China Biliary tract is infested by adult helminths or their ovaCauses:Trematodes (Liver or biliary flukes): Most CommonClonorchis sinensisOpisthorchis viverrini or O. felineusFasciola hepaticaNematode (Ascaris lumbricoides by intraductal migration of adult worm)