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': 'Which of the following reduces the development of unexposed Ag halide crystals, and also acts as antifog agent? \nSelect and explain. \nA. Phenidone, B. Potassium hydroxide, C. Sodium sulfite, D. Sodium bromide', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]