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': 'The sterility of the root canal during treatment is assessed by \nSelect and explain. \nA. Radiographs, B. Clinical observations, C. Bacterial cultures, D. Colour of dressings', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]