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
In the formula for urea clearance, C = U x V/P, what does U stands for: 
Select and explain. 
A. Urinary concentration in g/24 hour, B. Urinary concentration in mg/ml, C. Urine osmolarity, D. Urine volume per minute
B: Urinary concentration in mg/ml
Answer: B: Urinary concentration in mg/ml 
Explanation: Ans: B. Urinary concentration in mg/ml(Ref: Ganong 25/p p676. 21/c p678)In given formula for measuring GFR:C = Clearance of the substanceU = Urinary concentration of the substance in mg/mlP = Plasma concentration of the substance in mg/mlV = Volume of urine