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': 'Linear depression on a tooth surface \nSelect and explain. \nA. Pit, B. Groove, C. Fossa, D. Sulcus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]