This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamins and Minerals, Subject name: Biochemistry
Folinic acid is: 
Select and explain. 
A. 5-formyl tetrahydrofolate, B. 5-formyl dihydrofolate, C. N5, N10-methylene tetrahydrofolate, D. N5, N10-methylene dihydrofolate
A: 5-formyl tetrahydrofolate
Answer: A: 5-formyl tetrahydrofolate 
Explanation: * Folinic acid is 5-formyltetrahydrofolate. It is also known as leucovorin and citrovorum factor. * Folinic acid can be directly conveed to N5, N10-methylene tetrahydrofolate. Extra:-When methotrexate is used for chemotherapy, normal cells are also affected. * Folinic acid is administered to rescue the normal cells from the toxic effect of methotrexate.