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': 'Incubation period of typhoid -a)  3-20 daysb)  14-45 daysc)  5-10 daysd)  15-60 dayse) 10-14 days \nSelect and explain. \nA. ae, B. b, C. ab, D. ad', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]