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
Trimethoprim acts by: 
Select and explain. 
A. Inhibiting peptidyl transferase enzyme, B. Inhibiting dihydrofolate reductase enzyme, C. Inhibiting Dihydropteroate synthase enzyme, D. Binds to 50s ribosomal unit and prevents protein synthesis
B: Inhibiting dihydrofolate reductase enzyme
Answer: B: Inhibiting dihydrofolate reductase enzyme 
Explanation: Trimethoprim, Methotrexate and pyrimethamine inhibits dihydrofolate reductase enzyme and prevents formation of Tetrahydrofolic acid and from Dihydrofolic acid.