The right answer is C.
ATP is a key molecule of cellular energy
Living beings derive their energy from the oxidation of nutrients, and this is true even for chlorophyllous plants (which use the energy of photons to make organic matter that can be oxidized later). However, the energy released during this oxidation is not directly usable by the cells. It is captured by an intermediary who, in the vast majority of cases, turns out to be the ATP. Indeed, very many cellular events or energetically unfavorable metabolic reactions can take place thanks to the rupture of the energy-rich phosphodiester bond of an ATP molecule.
In the cell, stocks of ATP are small, so the molecule must be continually renewed. Cellular respiration, involving mitochondria, allows the formation of new ATP molecules. In plants, photosynthesis also produces ATP in chloroplasts.