Answer: a.autotrophs
Step-by-step explanation:
Autotrophs and heterotrophs are in equilibrium in the biosphere: Autotrophs capture sunlight to form ATP and NADPH, molecules they use to produce organic compounds from CO2 and H2O and release O2 into the atmosphere. Heterotopic beings, in turn, consume the organic compounds produced by autotrophic beings to obtain energy by oxidizing these compounds using atmospheric O2 and releasing CO2 into the environment. CO2 is used again by autotrophs, closing the cycle.