In class one day, a student heard the teacher say that "like dissolves like." To test this theory, she performed the following
experiment:
Four 250 mL beakers containing 100 mL of water each were placed side by side on a table.
Then, she put 50 g sodium chloride, 50 g vegetable oil, 50 g sugar, and 50 g glycerin into the first, second, third, and fourth
beakers, respectively.
Finally, she stirred each beaker for exactly 2 minutes using a different stirring rod for each beaker.
Which of the following factors was the variable in her experiment?
A. the volume of the water
B. the quantities of the substances
C. the substances that were placed in the water
D.
the time that she stirred each beaker