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: Dental
[{'content': 'Which stage of syphilis is most contagious ? \nSelect and explain. \nA. Primary, B. Secondary, C. Early latent, D. Later latent', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]