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: Microbiology
[{'content': 'Organism causing biliary tract obstruction: \nSelect and explain. \nA. Clonorchis sinensis, B. Ankylostoma duodenale, C. Strongyloides stericoralis, D. Enterobius vermicularis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) Clonorchis sinensis', 'role': 'assistant'}]