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': 'The most important source of infection for meningococci - \nSelect and explain. \nA. Case, B. Subclinical case, C. Carriers, D. Latent case', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]