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': 'True statement regarding diptheria is - \nSelect and explain. \nA. It can be diagnosed by demonstration of antibodies by ELISA, B. Immunisation prevents carriers state, C. Treatment of contacts is not indicated, D. Iron has critical value in the production of toxin', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]