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
The plaque removal effectiveness of powered toothbrush over manual toothbrush is best explained by 
Select and explain. 
A. Sonic effect, B. Acoustic streaming, C. Hawthorne effect, D. Ultrasonic effect
C: Hawthorne effect
Answer: C: Hawthorne effect 
Explanation: None