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': "Gingival crevicular fluid is measured using: \nSelect and explain. \nA. Whatman's filter paper, B. Ph paper, C. Mylar strip, D. Litmus paper.", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]