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
Gold standard study for Clinical research is 
Select and explain. 
A. Randomised double-blind trial, B. Systematic meta-analysis, C. Ecological study, D. Retrospective cohort study
B: Systematic meta-analysis
Answer: B: Systematic meta-analysis 
Explanation: • Meta-analysis (Highest clinical relevance: GOLD STANDARD)
• Systematic review
• Cohort study
• Case control study
• Case series
• Case report
• Ideas, Editorials, Opinions
• Animal research
• In-vitro (test-tube) research (Lowest clinical relevance)