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: Dental
[{'content': 'Hedstroem file is an instrument used for \nSelect and explain. \nA. Canal enlargement, B. Length determination, C. Obturating with gutta percha in McSpadden technique, D. Endodontic implants', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]