The site of photosynthesis is chloroplasts, so green plants only perform photosynthesis in the parts containing chloroplasts. Leaves are composed of epidermis, mesophyll and veins. Mesophyll cells contain a large number of chloroplasts, which are responsible for photosynthesis. The main part; the green part of the young stem can also perform photosynthesis, so the main organ of green plants for photosynthesis is the leaf.

So choose: C