Narrative (refer to question(s) below): In the Sonoran Desert of the southwestern United States, scientists observed that population clusters of a small cactus were pronounced around nests of desert woodrats. Given this spatial relationship, they began to think the woodrat was related to the seeding of these cactus plants.

After years of counting and observing woodrat nests and nearby cactus plants, scientists collected woodrat droppings for laboratory analysis to determine whether they contained cactus seeds. They also collected the droppings and transported them to other areas to see if this would bring about new population clusters of the cactus.

Scientists then programmed the data they had collected into a computer. A computer program enabled them to predict that increases in the woodrat population would result in corresponding increases in the cactus population, and likewise, a decrease in the number of woodrats would signal an impending decrease in cactus.

Which phase of the study could be described as modeling?

A. when the scientists first observed the proximity of woodrat nests and cactus plants

B. when the scientists first wondered whether or not woodrats were connected to the seeding of cactus plants

C. when the scientists carried out laboratory analysis to generate data about the woodrat droppings

D. when the scientists determined from computer programs how woodrat nest numbers would impact cactus populations

E. when the scientists transported woodrat droppings to other areas in the field