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: Social & Preventive Medicine
[{'content': 'Positive schick test indicates \nSelect and explain. \nA. Person is susceptible to syphilis, B. Person has immunity to syphilis, C. Person is susceptible to Diphtheria, D. Person has immunity to Diphtheria', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]