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: Physiology
The vitamin that is most necessary for maturation of red blood precursor cells is: 
Select and explain. 
A. Folic acid., B. Cyanocobalamine, C. B6., D. B1.
B: Cyanocobalamine
Answer: B: Cyanocobalamine 
Explanation: Cyanocobalamine, folic acid, pyridoxine are essential for haematopoiesis, while cyanocobalamine is the most necessary one.