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
Most difficult criterion to establish Causal Association in aetiology of a disease is 
Select and explain. 
A. Specificity of association, B. Strength of association, C. Temporality, D. Biological plausibility
A: Specificity of association
Answer: A: Specificity of association 
Explanation: None