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 overall degree of darkness of an exposed film is known as: \nSelect and explain. \nA. Radiographic contrast, B. Radiographic density, C. Brightness, D. Exposure', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]