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
The 5th key to normal occlusion is: 
Select and explain. 
A. Molar interarch relationship, B. Mesiodistal crown angulations, C. Absence of rotation, D. Tight contacts
D: Tight contacts
Answer: D: Tight contacts 
Explanation: None