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
Test for estimating kidney function is: 
Select and explain. 
A. Serum creatinine, B. Serum phosphatase, C. Inulin test, D. Insulin test
C: Inulin test
Answer: C: Inulin test 
Explanation: None