In which of these systems can parts of the oxygen cycle be found?

A. Atmosphere

B. Biosphere

C. Geosphere

D. Hydrosphere

The oxygen cycle can be found in all but the geosphere. There's oxygen in the atmosphere, so it has to be there, and the biosphere includes living things, which breathe oxygen, and water (hydrosphere) is made up of partly hydrogen, so there has to be oxygen there as well.