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
Fluoroquinolones act by which of the following mechanism: 
Select and explain. 
A. By inhibiting DNA gyrase., B. By inhibiting RNA polymerase., C. Inhibiting folic acid synthesis., D. Inhibiting protein synthesis.
A: By inhibiting DNA gyrase.
Answer: A: By inhibiting DNA gyrase. 
Explanation: These drugs act by inhibiting DNA gyrase (topoisomerase II) and topoisomerase IV resulting in the inhibition of DNA replication.