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': 'Radius of action of toxins in the bacterial plaque is \nSelect and explain. \nA. Less than 2.5 mm, B. Greater than 3.5 mm, C. Less than 1.5 mm, D. 1.5 - 2.5 mm', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]