This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Which of the following antineoplastic and immunosuppressant drugs is a dihydrofolate reductase inhibitor ? 
Select and explain. 
A. Methotrexate, B. Adriamycin, C. Vincristine, D. Cyclophosphamide
A: Methotrexate
Answer: A: Methotrexate 
Explanation: None