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': 'Citric acid is applied to root surface: \nSelect and explain. \nA. To reduce caries, B. To reduce sensitivity, C. To facilitate collagen fibre adhesion on to root surface, D. None of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]