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
Farmer's reducer is: 
Select and explain. 
A. Potassium sulfite + Sodium sulphate, B. Potassium ferricyanide + Sodium thiosulphate, C. Potassium sulfite + Sodium hydroxide, D. All of the above
B: Potassium ferricyanide + Sodium thiosulphate
Answer: B: Potassium ferricyanide + Sodium thiosulphate 
Explanation: 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.