The correct option is A Reduction
In Calvin cycle, the carboxylation step is achieved by the enzyme, ribulose- 1,5-bisphosphate carboxylase/oxygenase, also known as RuBisCO (rubisco). This enzyme combines carbon dioxide dissolved in the cytosol with ribulose- 1,5-bisphosphate (RuBP) to produce 3-phosphoglycerate (3-PGA). The 3-phosphoglycerate kinase adds a phosphate from ATP to the 3-PGA to make 1,3-bisphosphoglycerate. Then NADP (glyceraldehyde-3-phosphate dehydrogenase) removes hydrogen from NADPH and adds it to the 1,3-bisphosphoglycerate to make glyceraldehyde-3-phosphate (PGAL). So, PGAL is formed by the addition of H2 atom and hence this reaction is called as a reduction reaction.