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
When a dentist says that " I cannot fix your teeth if you do not open your mouth wide:" He is employing: 
Select and explain. 
A. Problem ownership., B. Voice control, C. Tolerance., D. Flexibility.
A: Problem ownership.
Answer: A: Problem ownership. 
Explanation: Problem ownership:

Negative messages like 'You must sit still'; undermine the rapport between child and dentist. "You" messages carry the implication that the child is wrong.
Instead "I" messages increase the flow of information. Eg: I cannot fix your teeth if you do not open your mouth wide. This is called problem ownership.