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': 'The use of long cone is adjunct in parallel technique: \nSelect and explain. \nA. To minimize the superimposition of anatomical structures, B. To prevent the shortening of image, C. To prevent the distortion of image, D. To prevent the elongation of image', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]