This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'The parameter that changes with advancement of age \nSelect and explain. \nA. Hematocrit, B. Creatinine clearance, C. Both, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The hemoglobin concentration, red blood cell count, and hematocrit value began to decrease in men in their sixth decade and in women in their seventh decade and the change was more prominent with advancing age, especially in men. The white blood cell count and platelet count tended to decrease with advancing age. Ref: guyton and hall textbook of medical physiology 12 edition page number: 116,117,118', 'role': 'assistant'}]