<prompt> In the treatment of undiagnosed megaloblastic anemia, vitamin B12 and folic acid should be given together because:Vitamin B12 acts as a cofactor for dihydrofolate reductaseFolic acid alone causes improvement of anemic symptoms but neurological dysfunction continues.Vitamin B12 deficiency may result in methylfolate trapFolic acid is required for conversion of methylmalonyl-CoA to succinyl CoA.  <response>: Ans. B Folic acid alone causes improvement of anemic symptoms but neurological dysfunction continuesRef: Katzung 10e p532; KDT 8e p656Vitamin B12 is required for conversion of methionine to homocysteine and for formation of succinyl CoA from methylmalonyl CoA.Deficiency of vitamin B12 results in megaloblastic anemia, GI manifestations and neurological abnormalities due to demyelination.Folic acid alone will correct the symptoms of megaloblastic anemia but it does not prevent neurological abnormalities, which continue to proceed.Neurological abnormalities manifests initially in the form of loss of posterior column sensations vibration, proprioception etc., but later on can result in subacute combined degeneration of spinal cord. 