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': "Farmer's reducer is: \nSelect and explain. \nA. Potassium sulfite + Sodium sulphate, B. Potassium ferricyanide + Sodium thiosulphate, C. Potassium sulfite + Sodium hydroxide, D. All of the above", 'role': 'user'}, {'content': "Answer: B \nExplanation: Farmer's Reducer is composed of separate solutions of Potassium Ferricyanide and Sodium Thiosulfate (plain hypo). These are usually combined just before use or are used as a two bath treatment.", 'role': 'assistant'}]