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
[{'content': 'For cephalometric projection, what should be the distance between source and the subject? \nSelect and explain. \nA. 5 feet, B. 6 feet, C. 7 feet, D. 9 feet', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Distance between source and the subject = 5 feet.\nDistance between film and the subject\xa0= 15 cm.', 'role': 'assistant'}]