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
If a bacteria were susceptible to both penicillin and Erythromycin, then it would not be appropriate to treat the patients with both antibiotics at the same time because 
Select and explain. 
A. Penicillin is inactivated by erythromycin, B. Erythromycin exerts its effects extracellularly, C. Erythromycin enhances the β-lactamases activity, D. Penicillin is only effective against growing cells
D: Penicillin is only effective against growing cells
Answer: D: Penicillin is only effective against growing cells 
Explanation: None