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 concavity at the root of the nose is used as a third point of reference with 
Select and explain. 
A. Whipmix average axis facebow, B. Hanau, C. Dentatus, D. Kayo
A: Whipmix average axis facebow
Answer: A: Whipmix average axis facebow 
Explanation: None