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
What is the clearance of a substance, if its concentration in plasma in 10 mg%, concentration in urine is 100 mg% and urine flow is 2 ml/min 
Select and explain. 
A. 0.2 ml/min, B. 0.2 ml/min, C. 2 ml/min, D. 20 ml/min
D: 20 ml/min
Answer: D: 20 ml/min 
Explanation: Clearance = urine flow rate ✕ urine concentration / plasma concentration
= 100 X 2 / 10
= 20 ml/min