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
Principle of health education includes 
Select and explain. 
A. Interest, B. Know to unknown, C. Good human relations, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Principle of health education :

Interst.
Credibility.
Participation.
Motivation.
Reinforcement.
Learning by doing.
Comprehension.
Known to unknown.
Setting an example.
Good human relations.
Feedback.
Leaders.