Vein because they have valves to prevent back flow of blood.
Answer:
Volume
Explanation:
The boiling point and density of water never changes, no matter how much you add
So the answer CAN'T be Boiling point or Density
Electrical Conductivity changes <em>only when the number of ions in a solution changes</em>
So it CAN'T be Electrical Conductivity
It has to be VOLUME because volume is the only physical property that changes when you add or take away liquid from a liquidous mixture
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