Answer: d. Cytosol
Step-by-step explanation:
The highly organized system of membranes in chloroplasts is essential to the functioning of photosynthesis. These three components are part of plant chloroplasts:
Thylakoids - Internal membranes of chloroplasts that have sac-like organizations.
Grana - When those thylakoids are combined in piles, stacked on top of one another we call them Grana.
Stroma - The semiliquid membrane system enclosing the thylakoid that houses enzymes required to accumulate carbon molecules.
While all those components are part of plant chloroplasts, the cytosol is part of the largest of the internal membranes of eukaryotic cells, called endoplasmic reticulum (ER). More specific it is the region exterior of the ER, while the inner region is called the cisternal space.