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
Tetracycline acts on: 
Select and explain. 
A. 30S ribosomes, B. 50S ribosomes, C. Cell membrane, D. Inhibiting DNA gyrase
A: 30S ribosomes
Answer: A: 30S ribosomes 
Explanation: None