This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemotherapy, Subject name: Pharmacology
[{'content': 'Leucovorin is used to decrease the toxicity of \nSelect and explain. \nA. Methotrexate, B. 6-Mercaptopurine, C. Thio-TEPA, D. Cytosine arabinoside', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref: Katzung 10th/887; KDT 6/e 823 Toxicity of methotrexate can be reversed by the administration of 5-formyltetrahydrofolate (leucovorin or citrovorum factor). Folic acid in the diet is in dihydrofolate form. It is ineffective in reversing methotrexate toxicity.', 'role': 'assistant'}]