Answer
A) amount of solute
Explanation
Dilution is adding more solvent to a solution to decrease the concentration of solute in a solution. The amount of solute does not change although the concentration, amount of solvent and the total volume does change.
An example of this would be adding more water (solvent) to lemonade to decrease the concentration of lemon juice (solute). Obviously this would increase the total volume because you are adding more water to the solution.
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