This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, 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: Experimental studies intervention studies include: Randomized control trials Field trials Community trials Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 70