How is carbon exchanged between the geosphere and biosphere to maintain life?

The biogeochemical cycle in which carbon is exchanged between Earth’s terrestrial biosphere, hydrosphere, geosphere, and atmosphere is called the carbon cycle. The global carbon budget is the balance of the fluxes of carbon between these four reservoirs. The terms source or sink define whether the net carbon flux is out of or into the reservoir, respectively.

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.