In the Sonoran Desert of the Southwestern United States, Scientists

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 connected 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 excluded woodrats from several other areas without cactus plants, then collected woodrat droppings and added those to half of these areas to examine whether the droppings were associated with the growth of 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.
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What finding would suggest that the woodrats were spreading cactus seeds?

A) New populations of cactus plants grew in all of the areas studied.
B) Areas without woodrats did not have cactus plants even if woodrat droppings were added.
C) New populations of cactus plants grew in the areas with woodrat droppings, but not in the areas that did not have droppings.
D) Woodrats were able to get into all of the areas being studied regardless of whether there were cactus plants.
E) New populations of cactus plants grew in the areas without woodrat droppings, but not in the areas with woodrat droppings.