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
In Mount and Hume classification, what will be the site size of the following lesion? 
Select and explain. 
A. 2.1, B. 2.2, C. 3.1, D. 3.2
C: 3.1
Answer: C: 3.1 
Explanation: MOUNT AND HUME CLASSIFICATION 1998