Task: Text Categorization
Input (English): 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:  <0> Timidylate synthetase <1> Aromatase <2> Topoisomerase <3> Reverse transcriptase <4> Dihydrofolate reductase.
Output (English): pharmacology