What is the role of a keystone species?

Question

What is the role of a keystone species?

A	Limiting the abundance of a competitively dominant species
B	Populating the ecosystem to decrease diversity
C	Exploiting the key resources in an ecosystem
D(I think is this one)	Competitively dominant to other organisms in the ecosystem

Answer 1

D is correct;

A keystone species is an organism that helps define an entire ecosystem. Without its keystone species, the ecosystem would be dramatically different or cease to exist altogether.