The correct option is C Calvin
3-phosphoglyceric acid as first CO2 fixation product in algal photosynthesis was discovered by Calvin. He used radioactive 14C in algal photosynthetic studies. This led to the discovery that the first CO2 fixation product was a three-carbon organic acid. He also helped to mark out the complete biosynthetic pathway, hence it is named as Calvin Cycle. The first stable product identified was 3-phosphoglyceric acid (PGA), hence it is named as C3 pathway. Calvin cycle occurs in all photosynthetic plants whether they have C3 or C4 pathway.