13. A group of students want to investigate the effects of plant moisture on the growth of caterpillars. The
students fill three identical boxes with an equal number of a kind of leaf that caterpillars eat. The students
keep the leaves in the first box dry, spray the leaves in the second box with two sprays of water, and spray
the leaves in the third box with four sprays of water. The students then add four caterpillars to each box.
Every day the length of each caterpillar is measured and recorded, and the results are averaged. What is
the outcome/dependent variable in this experiment?
A. The number of leaves put in each box
B. The amount of water put on the leaves
C. The number of caterpillars in each box
D. The change in length of the caterpillars.