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
Randomized controlled trials are - 
Select and explain. 
A. Clinical trials, B. Preventive trials, C. Before and after comparison studies, D. Evaluation of Health Services
A: Clinical trials
Answer: A: Clinical trials 
Explanation: Ans. is 'a' i.e., Clincial trials