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
[{'content': 'Which of the following antimicrobial agents act solely on the gram positive bacterial cell wall : \nSelect and explain. \nA. Ciprofloxacin, B. Gentamicin, C. Tetracycline, D. Vancomycin', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]