Answer:
c. carbon source
Step-by-step explanation:
A "carbon source" refers to processes that hastens carbon release into the atmosphere more than what they absorb. Example of this is the burning of nonrenewable resources like fossil fuels.
The combustion of fossil fuels increases the release of carbon dioxide. Carbon is then being trapped into the atmosphere. This contributes to "global warming."
This is opposite to "carbon sink," which absorbs most of the carbon than they emit.