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
If the extension of a cavity from a primary groove towards the cusp tip is more than 2/3 then: 
Select and explain. 
A. No cusp capping., B. Consider capping., C. Cusp capping mandatory., D. None
C: Cusp capping mandatory.
Answer: C: Cusp capping mandatory. 
Explanation: If the extension of a cavity from a primary groove towards the cusp tip is