Concept:The dark stage of photosynthesis is the enzyme-driven fixation of carbon dioxide into organic sugars without a direct need for light.
Explanation:Photosynthesis occurs in two stages: the light stage and the dark stage.
The dark stage is also called the biosynthetic or assimilatory stage.
In this stage, atmospheric carbon dioxide,
CO2, is absorbed and reduced to sugars through a series of reactions.
These reactions do not require solar light directly, though they depend on ATP and NADPH produced in the light stage.
Photophosphorylation, photolysis of water, and excitation of chlorophyll are all light-dependent processes.
Therefore, the dark stage is specifically associated with the assimilation of Carbon(IV)oxide.
Answer:A. Assimilation of Carbon(IV)oxide