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
In a UK study, it was found that there were more deaths from Asthma than the sale of Anti-asthma drugs. This is an example of 
Select and explain. 
A. Cohort study, B. Case reference study, C. Ecological study, D. Experimental study
C: Ecological study
Answer: C: Ecological study 
Explanation: None