Answer:
D. leaves
Step-by-step explanation:
Photosynthesis reactions mainly occur in the leaves of plants.
Photosynthesis is the process by which plants and other photoautotrophs generate carbohydrates and oxygen from carbon dioxide, water and light energy in chloroplasts. Photosynthesis reactions mainly occur in the chloroplasts which is located in the mesophyll cells within the leaves of plants. Chloroplast is an organelle in plant cells that contains chlorophyll; a green pigment which absorbs light energy for plants to perform its photosynthesis reactions.