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
[{'content': '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 \nSelect and explain. \nA. Cohort study, B. Case reference study, C. Ecological study, D. Experimental study', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]