Answer:
The correct answer would be - location of plants and the watering schedule.
Explanation:
In this experiment, Stephen placed the pot of the flower in a sunny window, shady window, and dark closet and waters the sunny window pot and dark closet every day and shady window pot every other day.
In this experiment, plants receive more than one independent variable as there are many changes in subject plants like the type of water, conditions of pot watering schedule. For a better clear result, there should be all conditions should be constant except the one needs to study.