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': 'Intensity of radiation at a distance of 4 cm is R. At the distance of 2 cm, the intensity will be? \nSelect and explain. \nA. 1/2 R, B. R, C. 2 R, D. 4 R', 'role': 'user'}, {'content': "Answer: D \nExplanation: The intensity of an X-ray beam (the number of photons per cross sectional area per unit of exposure time) depends on the distance of the measuring device from the focal spot. For a given beam, the intensity is inversely proportional to the square of the distance from the source.\nWhite and Pharoah's Oral\xa0Radiology Principles and Interpretation 8th edition", 'role': 'assistant'}]