This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Malnutrition, Subject name: Pediatrics
Activity of glutathione reductase in RBCs gives an idea about functional index of which of the following? 
Select and explain. 
A. Riboflavin, B. Pyridoxine, C. Niacin, D. Biotin
A: Riboflavin
Answer: A: Riboflavin 
Explanation: Activity of glutathione reductase in RBCs gives an idea about functional index of flavin coenzyme activity- Riboflavin