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: Microbiology
[{'content': 'Most important element in treatment of diphtheria - \nSelect and explain. \nA. Antitoxin, B. Tetracycline, C. Erythromycin, D. Penicillin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]