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
A new drug is to be evaluated for its therapeutic effect. The best study design will be - 
Select and explain. 
A. Cross sectional survey, B. Case - control design, C. Natural experiment, D. Randomized controlled trial
D: Randomized controlled trial
Answer: D: Randomized controlled trial 
Explanation: RCT has questioned the validity of such widely used treatment as oral hypoglycemic agents, varicose vein stripping, tonsillectomy, hospitalization of all patients with myocardial infarction, multiphasic screening and toxicity and applicability of many preventive and therapeutic procedures. Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 89