This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
Incubation period of swine flu- 
Select and explain. 
A. 1-3 days, B. 2-3 weeks, C. 10-15 days, D. 5 weeks
A: 1-3 days
Answer: A: 1-3 days 
Explanation: (ref:Park's text book 23rd edition) Incubation period of swine flu is 2 - 3 days. It is caused by pandemic influenza A (H1N1) It can infect Lower respiratory tract and causes rapidly progressive pneumonia.