Scientists interested in knowing the best way to restore an area after a temporary road was built through it completed a study comparing two treatments: (1) restoring the contour of an area so that there was no longer a depression or cut-through where the road was previously and (2) simply abandoning the area to allow vegetation to return on its own. They wanted to know whether either or both of these treatments would return the above ground vegetation and the below ground soil properties to their original state, as seen in a similar area where there has never been a road. This study was focused on which level of life's hierarchy?
A. Organism
B. Community
C. Population
D. Ecosystem

The living beings and the non-living conditions of a region interact with each other. They together make an ecosystem. In the given study, the aim was to restore the above-ground vegetation of the region. The "above ground vegetation" of the region is part of its biotic factors. The "below ground soil" is a component of the abiotic factors of the region. Since the study focused on both biotic and abiotic factors of the region, it focused on the ecosystem.