The is the balance of the amount of carbon in each reservoir.
a. global nitrogen budget
b. global carbon budget
c. global oxygen budget
d. global respiration budget

Global carbon budget.

Explanation: The global carbon budget can be defined as the budget that balances the fluxes of carbon between the four reservoirs. These four reservoir of carbon are Earth's terrestrial biosphere, hydrosphere, atmosphere and geosphere.

The total amount of carbon on the earth should be maintained so there is a global carbon budget that maintains the amount of carbon on earth.