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': 'Which topical fluoride agent makes use of thixotrophic properties for better penetration into inter proximal areas? \nSelect and explain. \nA. Sodium fluoride solution, B. Fluoride foam, C. Acidulated phosphate fluoride gel, D. Fluoride varnish', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]