What are keystone species?

• A
  Common species that have a large biomass but have little and negligible impact on the community organization.
• B
  Rare species that have minimal impact on the biomass and other species in the community.
• C
  Dominant species that constitute a large proportion of biomass and affect many other species.
• D
  Species that make up only a small proportion of the total biomass of a community,yet have a large impact on the community organization and survival.