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
For the purpose of intervention trials, the preferred randomization unit is an individual for all of the following except 
Select and explain. 
A. Vaccine, B. Drug, C. Surgery, D. Health Education
D: Health Education
Answer: D: Health Education 
Explanation: .