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: Unknown
The need for vitamin B12 and folic acid in the formation of red blood cells is related primarily of their effects on: 
Select and explain. 
A. Synthesis and release of erythropoietin from the kidney, B. Absorption of iron from the gut, C. DNA synthesis in bone marrow, D. Hemoglobin formation in the red blood cell
C: DNA synthesis in bone marrow
Answer: C: DNA synthesis in bone marrow 
Explanation: Within 6-9 hours of treatment with vitamin B12 formation of nuclear DNA component promotes normoblastic reaction of the bone marrow. Folic acid also promotes the formation of nucleic acids.