Answer:
Independent Variable: The Electrolyte Drink
Dependent Variable: Concentration of electrolytes in their blood
Control Var 1: Measuring the concentration of electrolytes before drinking
Control Var 2: Using the same amount of drink for each player.
Control Var 3: Making sure they don't drink any extra water to dilute the concentration
I predict that of all the drinks, Gatorade will rank first, Powerade second, Propel third and vitamin water last.