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 antimicrobial agents act solely on the gram positive bacterial cell wall : 
Select and explain. 
A. Ciprofloxacin, B. Gentamicin, C. Tetracycline, D. Vancomycin
D: Vancomycin
Answer: D: Vancomycin 
Explanation: None