Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: The 2,4-diaminopteridine systems, such as aminopterin or methotrexate, are good antitumor agents since they reduce the biosynthesis of purines and pyrimidines by inhibiting the enzyme: 
 Options:  <1> Timidylate synthetase <2> Aromatase <3> Topoisomerase <4> Reverse transcriptase <5> Dihydrofolate reductase.
