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 antibiotic acts by inhibiting cell wall synthesis ? 
Select and explain. 
A. Chloramphenicol, B. Gentamicin, C. Erythromycin, D. Penicillin
D: Penicillin
Answer: D: Penicillin 
Explanation: None