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
Incubation period of syphilis is: 
Select and explain. 
A. 9-90days, B. 10-14days, C. 10-21days, D. 15-30days
A: 9-90days
Answer: A: 9-90days 
Explanation: None