Final answer:
The Calvin cycle occurs in the stroma of the chloroplast, which is the fluid space surrounding the thylakoid membranes, where the light-dependent reactions take place.
Step-by-step explanation:
The Calvin cycle, which is part of the light-independent reactions of photosynthesis, takes place in the stroma of the chloroplast. In contrast, the light-dependent reactions occur in the thylakoid membranes. The stroma is the fluid-filled space that surrounds the grana, where stacks of thylakoids are located. The enzymes necessary for the Calvin cycle are found within the stroma. Meanwhile, the thylakoid membranes contain photosystems I and II, as well as the enzyme NAD+ reductase, which are crucial for the light-dependent reactions. Therefore, the correct answer to the student's question is b) Stroma of the chloroplast.