Answer:
Option B, The amount of water in the blood
Step-by-step explanation:
This can be understood from the scenario as described below – 
Suppose the quantity of water (volume by volume, v/v or %) in blood is equal to X litre which constitute Y% of the total blood volume. 
Then, the volume of blood can be determined in the following ways- 
Y % of blood volume is equal to X liters 
Then 
 
![(Y)/(100)  * Blood Volume [tex]= X\\](https://img.qammunity.org/2017/formulas/biology/high-school/1wu8ea68lc14y783g2j0pgfoglkb10z0nv.png) litres
 litres
Blood Volume 
 litres
litres
Thus, in this way if amount of water in blood is known, then the blood volume can be determined.