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': 'How does root caries appear in cross section? \nSelect and explain. \nA. Rhomboidal, B. U shaped, C. V shaped, D. Inverted V shaped', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Root caries: U\xa0shaped\nPit and fissure caries: Inverted V shaped\nSmooth surface caries: triangular/ cone shaped', 'role': 'assistant'}]