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
Most common source of Diphtheria- 
Select and explain. 
A. Case, B. Carrier, C. Both, D. None
B: Carrier
Answer: B: Carrier 
Explanation: Carriers are common sources of infection, their ratio is estimated to be 95 carriers for 5 clinical cases. Ref:PARK&;S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE 23rd edition , Page 160