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
Pandemic are caused by -a)  Hepatitis Bb)  Influenza-Ac)  Influenza-Bd)  Influenza-Ce) Cholera 
Select and explain. 
A. bd, B. be, C. bcd, D. da
B: be
Answer: B: be 
Explanation: None