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 thickness of rubber dam for children \nSelect and explain. \nA. 6 x 6", B. 3 x 3", C. 5 x 5", D. 8 x 8"', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]