Four 250 ml beakers containing 100 ml of water each were placed side by side on a table.

she then put 50 g sodium chloride , 50 g vegetable oil, 50 g sugar,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 experinent?

a. the quantities of the substances.

b. the time that she stirred the beaker.

c. the substances that were placed in water.

d. the volume of water.