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
Irregular concavity in the lingual surface of the incisors above the cingulum is known as: 
Select and explain. 
A. Fossa., B. Groove., C. Sulcus., D. Pit
A: Fossa.
Answer: A: Fossa. 
Explanation: None