The answer is c. Starch.
During photosynthesis in the leaves of the plants, carbon dioxide and water are converted into glucose and oxygen using the energy of sunlight. The excess of glucose synthesized in photosynthesis is converted and stored as a starch which is than transported into storage organs where it will serve as a long-term energy storage.
Fat is used for long-term energy storage in animals, while ATP and ADP are short-term energy storage.