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
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: None