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': 'Histological depth of the sulcus is represented by: \nSelect and explain. \nA. Gingival sulcus, B. Base of the gingival sulcus, C. Free gingival groove, D. None of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]