Final answer:
Controlled fires in North Carolina are primarily used to add nutrients to the soil and maintain healthy forest ecosystems, particularly by supporting fire-adapted species like the jack pine. Option C is correct.
Step-by-step explanation:
One reason why controlled fires are used in North Carolina is to maintain biodiversity and ecosystem services. Controlled fires help by opening seed cones of fire-adapted species like the jack pine, adding nitrogen to the soil, and reducing undergrowth to limit competition among plant species.
While one might think they also serve to eliminate pesticide chemicals, the primary ecological purpose is to regenerate the habitat and keep forest ecosystems healthy. Though not explicitly listed among the options, the closest correct choice related to the reasons provided would be Option C: to keep rich nutrients in the soil, since fire returns nutrients to the soil and helps maintain the nutrient cycle.