Question

which species were reintroduced to yellowstone national park that had a overall positive impact there?
wolves
beavers
elk
herons

Explanation:

The reintroduction of wolves to Yellowstone National Park led to a trophic cascade, improving the ecosystem by controlling elk populations, which in turn benefited vegetation, beavers, and other species. Beavers, elk, and herons were not the reintroduced species with this key positive impact.

Answer:

A. Wolves