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': "Toxigenicity of C. diphtheria is determined by- \nSelect and explain. \nA. Elek's gel ppt test, B. Aselole's reaction, C. Nagler's reaction, D. All", 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Elek's gel ppt test", 'role': 'assistant'}]