Which one of the following statements best reflects the overall position of current science on the role of biodiversity in ecosystems?

• A.  The more species in an ecosystem, the greater the biomass production.
• B.  The more species in an ecosystem, the greater the drought resistance.
• C.  The effects of biodiversity on the functioning of an ecosystem are not consistent.
• D.  Almost every species in an ecosystem is essential to maintain the overall ecosystem.