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': 'Contrast in X-rays is dependent on: \nSelect and explain. \nA. KV, B. mA, C. Duration of exposure, D. Distance between source and object', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. KV', 'role': 'assistant'}]