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
Study of alcohol intake for 20 years and occuring of liver disease is a type of 
Select and explain. 
A. Cohort study, B. Case control study, C. Ecological study, D. RCT
A: Cohort study
Answer: A: Cohort study 
Explanation: None