Which organisms are an example of a keystone species? select 3

Lions, Jagurs, Gray wolf, Sea otters, Sea stars, American alligators, Bees, Sharks, African Elephants, Snowshoe Hare, Beavers, Bears, Bats, Hummingbird

i am going to guess that it is co2.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.