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': 'Value of total filtration for 70 kVp is: \nSelect and explain. \nA. 2.1 mm, B. 2.3 mm, C. 1.5 mm, D. 2.5 mm', 'role': 'user'}, {'content': "Answer: C \nExplanation: 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'}]