What are the three main reservoirs of the oxygen cycle? A. atmosphere, the water cycle and rocks B. biosphere, the water cycle and rocks C. atmosphere, the biosphere and the water cycle D. atmosphere, the biosphere and rocks

I would say C b/c rocks are as useless as well ... rocks ...

Most likely C because the Biosphere is living things and what do most living things need to breathe? Atmosphere because the atmosphere is made up of air. The water cycle because through evaporation you need air for the water to evaporate.