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: Medicine
[{'content': 'Chronic kidney disease is defined as GFR less than (mL/ min/ 1.73 m2): March 2004 \nSelect and explain. \nA. 60, B. 70, C. 80, D. 90', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A i.e. 60', 'role': 'assistant'}]