The correct answer is after the reduction step of the Calvin cycle (before the regeneration step of the starting molecule).
Calvin cycle is one the phases of photosynthesis, also known as light-independent reactions. During the cycle, CO2 is fixed and converted to three-carbon sugars. The process requires ATP and NADPH from the previous photosynthesis reactions (light dependent reactions).
The Calvin cycle is divided in three stages: fixation, reduction and regeneration.
