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 typically is: \nSelect and explain. \nA. 0.6 to 3.0, B. 0.2 to 0.3, C. 0.2 to 0.4, D. 0.6 to 4.0', 'role': 'user'}, {'content': 'Answer: B \nExplanation: An unexposed film, when processed, shows some density. This\xa0appearance is caused by the inherent density of the base and added\xa0tint and the development of a\xa0few unexposed silver halide crystals. This minimal density is called base plus fog and typically is 0.2 to 0.3. Radiographic density is influenced by exposure and the thickness and density of the subject.\nImage receptors in Oral and Maxillofacial Radiology, pg -16, White and Pharoah, 7th ed, pg- 75', 'role': 'assistant'}]