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 is an inhibitor of dihydrofolate reductase- 
Select and explain. 
A. Phenytoin, B. Alcohol, C. Methotrexate, D. Yeast
C: Methotrexate
Answer: C: Methotrexate 
Explanation: Ans. is 'c' i.e., Methotrexate o Methotrexate is folate antagonist : inhibits dihydrofolate reductase (DHP Rase) - blocking the conversion of dihydrofolic acid to tetrahydrofolic acid which is an essential co-enzyme required for one carbon transfer reactions in de novo purine synthesis and amine acid interconversions.