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
[{'content': 'For the purpose of Intervention Trials, the preferred randomization unit is an individual for all of the following except - \nSelect and explain. \nA. Vaccine, B. Drug, C. Surgery, D. Health Education', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]