Answer:
A. cycled by carbon-fixing bacteria
Step-by-step explanation:
This process is also called "Biological carbon fixation."
Here is a more in-depth answer:
Biological carbon fixation or сarbon assimilation is the process by which inorganic carbon (particularly in the form of carbon dioxide) is converted to organic compounds by living organisms. The compounds are then used to store energy and as structure for other biomolecules.