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: Pathology
Which of the following is a stain for heart failure cells? 
Select and explain. 
A. PAS, B. Prussian blue, C. Sudan black, D. Oil red
B: Prussian blue
Answer: B: Prussian blue 
Explanation: Heart failure cells, also called siderophages, are hemosiderin-containing macrophages in the alveoli of lung and these cell denote previous episodes of pulmonary edema due to left-sided heart failure.
Hemosiderin is nothing else but stored iron granules.
So, heart failure cells contain iron granules and thus will require a stain that is used for iron.
Stain used for iron is Prussian blue reaction (Perl's iron stain)