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
Patient's head position while recording Potsdam by fluid wax technique should be: 
Select and explain. 
A. Frankfort horizontal plane is 15 degrees below the horizontal plane., B. Frankfort horizontal plane is 30 degrees below the horizontal plane., C. Frankfort horizontal plane is 45 degrees below the horizontal plane., D. None
B: Frankfort horizontal plane is 30 degrees below the horizontal plane.
Answer: B: Frankfort horizontal plane is 30 degrees below the horizontal plane. 
Explanation: None