This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hematology, Subject name: Pharmacology
Which of the following metabolic reactions require vitamin B12 but not folate? 
Select and explain. 
A. Conversion of malonic acid to succinic acid, B. Conversion of homocysteine to methionine, C. Conversion of serine to glycine, D. Thymidylate synthesis
A: Conversion of malonic acid to succinic acid
Answer: A: Conversion of malonic acid to succinic acid 
Explanation: This reaction is required for myelin formation and deficiency of B12 is responsible for demyelination. Other reactions in question requires THFA in addition to Vit B12.