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
Which of the following lead to an outbreak of Influenza in China in 2013 - 
Select and explain. 
A. H
1
N
1, B. H
3
N
2, C. H
2
N
2, D. H
7
N
9
D: H
7
N
9
Answer: D: H
7
N
9 
Explanation: In china, there was an outbreak of influenza caused by Avian influenza H7N9, in 2013.
It started in china and spread to Hong Kong.
Most common age group affected was older male (> 50 years).