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
Frankfort - horizontal is a reference plane constructed by joining which of the following landmarks? 
Select and explain. 
A. Nasion and Sella, B. Porion and Sella, C. Porion and Nasion, D. Porion and Orbitale
D: Porion and Orbitale
Answer: D: Porion and Orbitale 
Explanation: None