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
Influenza pandemic is mainly caused by- 
Select and explain. 
A. Type A, B. Type B, C. Type C, D. All
A: Type A
Answer: A: Type A 
Explanation: All known pandemics caused by influenza A strains. Ref:PARK'S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE 23rd edition , Page: 153