Select the formula for ecological efficiency.

• A
  $\frac{\text{Gross primary productivity}}{\text{Incident total solar radiation}} \times 100$
• B
  $\frac{\text{Food energy assimilated}}{\text{Food energy ingested}} \times 100$
• C
  $\frac{\text{Net primary productivity}}{\text{Gross primary productivity}} \times 100$
• D
  $\frac{\text{Energy in biomass production at trophic level } n}{\text{Energy in biomass production at previous trophic level } n-1} \times 100$