Ans. is 'a' i.e., Folic acid deficiency * Megaloblastic anemia is an anemia which results from inhibition of DNA synthesis during red blood cell production.* It is characterized by many large immature and dysfunctional red blood cells (megaloblasts) in the bone marrow, and also by hypersegmented neutrophills.* Vit B12 and folic acid are required for DNA synthesis. Any factor that results in deficiency of vit B12 or folic acid will lead to defective DNA synthesis. Inadequate DNA synthesis results in defective nuclear maturation. However, the synthesis of RNA and proteins is not altered, so cytoplasmic maturation proceeds in advance of nuclear maturation - Nuclear/Cytoplasmic asynchrony that results in formation of megaloblasts.Important causes of megaloblastic anemiaVitamin BJ2 deficiency* Decrease intake: Inadequate diet, vegetarianism.* Impaired absorption : Intrinsic factor deficiency (pernicious anemia, gastrectomy), intestinal diseases (crohn's disease, ileitis, ileal resection, lymphoma, systemic sclerosis), fish tapeworm infestation (D. latum), blind loop syndrome (bacterial overgrowth), diverticuli of bowel, chronic pancreatitis.* Increased requirment: Pregnancy, hyperthyroidism, disseminated cancer.Folate deficiency* Decrease intake: Inadequate diet, alcoholism, infancy.* Impaired absorption : Malabsorption state, intestinal diseases.* Increased requirment: Pregnancy, infancy, disseminated cancer.* Others : Hemodialysis, antifolate drugs (methotrexate, phenobarbitone, phenytoin, trimethoprim, primidone, triametrene, azathioprine.Rare causes* These are : Hereditary orotic aciduria, hypothyroidism, Di-Gueglielmo syndrome, congenital dyserythropoietic anemia, thiamine and pyridoxine deficiency.