Ans. (A). photosynthesis.
The green disks in Elodea plant cell under a microscope represent specialized plant cell organelles, known as chloroplasts. Chloroplasts are double-membrane bound cell organelles that contain green pigments or chlorophyll molecules.
These pigments trap the energy from solar light, which is used by the plants for the process of photosynthesis to make their food.
Thus, the correct answer is option (A).