<prompt> A new drug is to be evaluated for its therapeutic effect. The best study design will be -Cross sectional surveyCase - control designNatural experimentRandomized controlled trial  <response>: 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, Parks Textbook of Preventive and Social Medicine, Page no. 89 