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: Dental
Theories which define the etiology of thumb sucking: 
Select and explain. 
A. Sigmond Freud theory., B. Oral drive theory., C. Benjamin theory of rooting reflex., D. All of the above.
D: All of the above.
Answer: D: All of the above. 
Explanation: None