This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pathology
A reactant generated by neutrophils that plays an impoant role in bacterial killing is 
Select and explain. 
A. NADPH oxidase, B. Hexose monophosphate shunt, C. G proteins, D. Superoxide anion
D: Superoxide anion
Answer: D: Superoxide anion 
Explanation: Superoxide anion is generated when oxygen is reduced by cytoplasmic NADPH. The reduction is carried out by the enzyme NADPH oxidase, which is not a reactant but a catalyst activated in cells responding to bacteria.