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: Physiology
Which of the following does not changes in the old age 
Select and explain. 
A. GFR, B. Glucose tolerance, C. Haematocrit, D. Blood pressure
C: Haematocrit
Answer: C: Haematocrit 
Explanation: None