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
Histological depth of the sulcus is represented by: 
Select and explain. 
A. Gingival sulcus, B. Base of the gingival sulcus, C. Free gingival groove, D. None of the above
C: Free gingival groove
Answer: C: Free gingival groove 
Explanation: None