The correct option is C Oceans
Bulk CO2 fixation
Bulk CO2 fixation occurs in oceans, due to the majority of phytoplanktons which are microscopic plants floating in water bodies. They drift with water currents and live suspended in the water column.
The phytoplanktons form a major percentage of producers on this planet and are responsible for the fixation of a major bulk of CO2 available on earth into glucose by the process of photosynthesis.
Final answer
(B) Oceans