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: Radiology
In cephalometric radiography, the distance between the subject and the source of X-ray is 
Select and explain. 
A. 2 feet, B. 48 inches, C. 4.8 metres, D. 5 feet
D: 5 feet
Answer: D: 5 feet 
Explanation: By convention, the distance from the X-ray source to the subject's midsagittal plane is 5 feet.
Contemporary Orthodontics, William Proffit, 6th ed, pg-174