In the initial step in carbon fixation, a molecule of CO2 is attached to RuBP to produce a six-carbon molecule, which is immediately split to produce two molecules of 3-phosphoglycerate. After phosphorylation and reduction produces glyceraldehyde 3-phosphate (G3P), what more needs to occur to complete the Calvin cycle? A. addition of a pair of electrons from NADPH B. regeneration of ATP from ADP C. regeneration of RuBP D. regeneration of NADP+