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': 'Inherent filtration of X-ray machines: \nSelect and explain. \nA. 0.5-2 mm, B. 1.5-2 mm, C. 1.5-2.5 mm, D. 0.5-1 mm', 'role': 'user'}, {'content': "Answer: A \nExplanation: Inherent filtration consists of the materials that X-ray photons encounter as they travel from the focal spot on the target to form the usable beam outside the tube enclosure. These materials include the glass wall of the X-ray tube, the insulating oil that surrounds many dental tubes, and the barrier material that prevents the oil from escaping through the X-ray port. The inherent filtration of most X-ray machines ranges from the equivalent of 0.5 to 2 mm of aluminium. Added filtration may be supplied in the form of aluminium disks placed over the port in the head of the X-ray machine.\xa0 Total filtration is the sum of the inherent and added filtration. Governmental regulations require the total filtration in the path of a dental X-ray beam to be equal to the equivalent of 1.5 mm of aluminum for a machine operating at up to 70 kVp and 2.5 mm of aluminum for machines operating at higher voltages.\nReference: White and Pharoah's Oral Radiology Principles and Interpretation 7th edition page no 10,11", 'role': 'assistant'}]