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
[{'content': 'The plaque removal effectiveness of powered toothbrush over manual toothbrush is best explained by \nSelect and explain. \nA. Sonic effect, B. Acoustic streaming, C. Hawthorne effect, D. Ultrasonic effect', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]