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: Dental
The common first approach to test causal hypothesis is 
Select and explain. 
A. Descriptive study, B. Case-control study, C. Cohort study, D. Randomized controlled trial
B: Case-control study
Answer: B: Case-control study 
Explanation: None