Sally wants to know why the leaves of her plants are turning yellow. she suspects it is because the plants are not receiving enough nutrients. to test her hypothesis, she devises the following experiment. first, sally obtains four identical green plants. then, she places each plant in separate, but identical pots, with the same type and amount of soil. although sally gives each plant the same amount of water and sun exposure each day, she changes the amount of fertilizer placed in each pot. finally, she records the number of yellow leaves that she sees in each pot every day over the course of one month. what is the dependent variable in sally's experiment? a. the number of yellow leaves b. the type of green plant c. the amount of water d. the amount of fertilizer