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 optical density of gross fog is: \nSelect and explain. \nA. 0.6-3.0, B. 0.2-0.3, C. 0.2-0.6, D. None of the above', 'role': 'user'}, {'content': "Answer: B \nExplanation: An unexposed film, when processed, shows some density. This appearance is caused by the inherent density of the base and added tint and the development of a few unexposed silver halide crystals. This minimal density is called base plus fog and typically is 0.2 to 0.3.\xa0\n\xa0\nWhite and Pharoah's Oral\xa0 Radiology Principles and Interpretation 8th edition", 'role': 'assistant'}]