Fact 1: Biomass is the total mass of organisms at a trophic level.

Fact 2: Fourty percent of biomass is carbon.

Given the two facts above, answer the question "what are organisms mostly made out of?" with the following options: 
- limestone
 - food
 - energy
 - rock
 - bacteria
 - matter
 - carbon
 - fat


 

       carbon  